英语词汇“gemmule”造句的方法、技巧、例句及翻译-英语例句辞典

Darwin's “gemmule” theory—that hereditary instructions were thrown adrift by all cells and then floated in the blood, like a million messages in bottles—suggested that blood transfusions might transmit gemmules and thereby alter heredity. The Gene 2016-06-02T00:00:00Z

Gemmules secreted by the hand carried the instructions to manufacture a new hand; gemmules dispersed by the ear transmitted the code to build a new ear. The Gene 2016-06-02T00:00:00Z

Darwin imagined that the cells of all organisms produce minute particles containing hereditary information—gemmules, he called them. The Gene 2016-06-02T00:00:00Z

Galton tried transfusing rabbits with the blood of other rabbits to transmit the gemmules. The Gene 2016-06-02T00:00:00Z

If gemmules existed, then a mouse with a surgically excised tail should produce a mouse without a tail. The Gene 2016-06-02T00:00:00Z

In 1883, with rather grim determination, the German embryologist August Weismann had performed an experiment that directly attacked Darwin's gemmule theory of heredity. The Gene 2016-06-02T00:00:00Z

An atypical type of asexual reproduction is found only in freshwater sponges and occurs through the formation of gemmules. Gemmules are environmentally resistant structures produced by adult sponges wherein the typical sponge morphology is inverted. Fundamentals of Biology 2015-01-01T00:00:00Z

A type of asexual reproduction found only in freshwater sponges occurs through the formation of gemmules, clusters of cells surrounded by a tough outer layer. Concepts of Biology 2013-04-25T00:00:00Z

Statoblasts, hibernacula, and gemmules are alike produced asexually, but they resemble the eggs of Hydra in being provided with a hard, resistant shell, and in having the capacity to lie dormant until favourable conditions return. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

The result is then, with the worst-endowed families, that the "gemmules" or latent forces of hundreds of virtuous, or at least, not vicious, generations, lie hid in their constitutions. The Dangerous Classes of New York And Twenty Years' Work Among Them

If the whole ovum, about 1⁄150 in diameter, were all gemmules, the number would be sufficient to last, at this rate, one per second for 5,600 years! Was Man Created?

In freshwater sponges, gemmules may survive hostile environmental conditions like changes in temperature and serve to recolonize the habitat once environmental conditions stabilize. Fundamentals of Biology 2015-01-01T00:00:00Z

These granules for the sake of distinctness may be called cell-gemmules, or, as the cellular theory is not fully established, simply gemmules. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

Internally the gemmule consists of a mass of cells containing food-material in what may be called a tabloid form, for it consists of minutely granular plate-like bodies. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

Combination in various degrees between these gemmules is supposed to influence their appearance or non-appearance in the offspring at various stages. Life of Charles Darwin

On the contrary, in all ordinary cases of mutilation the purely atavistic elements or gemmules would be set free from any modifying influence of the non-existent or mutilated part. Are the Effects of Use and Disuse Inherited? An Examination of the View Held by Spencer and Darwin

Since gemmules can withstand harsh environments, are resistant to desiccation, and remain dormant for long periods, they are an excellent means of colonization for a sessile organism. Fundamentals of Biology 2015-01-01T00:00:00Z

The gemmules in each organism must be thoroughly diffused; nor does this seem improbable considering their minuteness, and the steady circulation of fluids throughout the body. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

The gemmules of sponges growing in lakes are sometimes deficient in spicules. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

A provisional hypothesis supplementing "Natural Selection."—Statement of the hypothesis.—Difficulty as to multitude of gemmules.—As to certain modes of reproduction.—As to formations without the requisite gemmules.—Mr. On the Genesis of Species

The gemmules—as in Galton's theory of heredity and with neuter insects—might be perfectly independent of pangenesis and the normal inheritance of acquired characters. Are the Effects of Use and Disuse Inherited? An Examination of the View Held by Spencer and Darwin

It is supposed that fecundation is chiefly necessary to give to the gemmules the requisite amount of nourishment to insure development. Plain Facts for Old and Young

So it must be with the gemmules of plants, for with certain kinds even a minute fragment of a leaf will reproduce the whole. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

The gemmules with their various coverings are usually spherical in shape, but in some species they are oval or depressed in outline. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

Therefore in many of such lower organisms such a congeries of ancestral gemmules must exist in every part of their bodies, since in them every part is capable of reproducing by gemmation. On the Genesis of Species

Hence, when the germs or gemmules which achieve development are either better or worse than the residue, the qualities transmitted to offspring will be of an inverse character. Are the Effects of Use and Disuse Inherited? An Examination of the View Held by Spencer and Darwin

The gemmules must be very small indeed, but it may be suggested that the molecules of matter are smaller still, so this fact is no objection to the theory. Plain Facts for Old and Young

On the other hand, it does not seem improbable that certain gemmules, under favourable conditions, should be retained and go on multiplying for a longer period than others. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

The period for which the gemmule lies dormant probably depends to some extent upon environment and to some extent on the species to which it belongs. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

The gemmules possess two sorts of affinity, one of which might be called propagative, and the other germinative affinity. On the Genesis of Species

Many obvious facts compelled Darwin to suppose that vast numbers of the reproductive gemmules in an individual are not thrown off by his own cells, but are the self-multiplying progeny of ancestral gemmules. Are the Effects of Use and Disuse Inherited? An Examination of the View Held by Spencer and Darwin

A third—It may be all caused by infinitely numerous p. xxviii“gemmules:” but his reason asks him—What puts infinite order into these gemmules, instead of infinite anarchy? Westminster Sermons with a Preface

In a highly organised and complex animal, the gemmules thrown off from each different cell or unit throughout the body must be inconceivably numerous and minute. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

The gemmules are single and closely adherent at the base of the sponge. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

We have seen also that in certain cases a similar multitude of gemmules must be included also in every considerable part of the whole body of each organism, but where are we to stop? On the Genesis of Species

If brain-work attracts, develops and sterilizes the best gemmules, the ultimate effect of education on the intellect of posterity may differ from its immediate effect. Are the Effects of Use and Disuse Inherited? An Examination of the View Held by Spencer and Darwin

According to this, every cell of every tissue and organ of the body produces minute particles called gemmules, which partake of the characters of the cells that produce them. The Doctrine of Evolution Its Basis and Its Scope

But this non-diffusion of the gemmules from bud to bud may be only apparent, depending, as we shall hereafter see, on the nature of the first-formed cells in the buds. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

The gemmules were noted and referred to as seeds. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

What wonder then that such an excessively complex body should divide and multiply; and what parity is there between such a body and a gemmule? On the Genesis of Species

Perhaps we might retain Darwin's self-multiplying gemmules without supposing them to be thrown off by the cells, which will no longer be credited with two modes of multiplication. Are the Effects of Use and Disuse Inherited? An Examination of the View Held by Spencer and Darwin

He argues that it is the undeveloped germs or gemmules of the fertilised ovum that form the sexual elements of the offspring, and thus heredity and atavism are explained. Alfred Russel Wallace: Letters and Reminiscences, Vol. 2

The assumed elective affinity of each gemmule for that particular cell which precedes it in the order of development is supported by many analogies. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

Microscleres Smaller spicules that lie free in the substance or the derma of the sponge, or are associated with the gemmule. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

For how can gemmules attach themselves to others to which they do not normally or generally succeed? On the Genesis of Species

The theory of pangenesis, as propounded by Mr. Darwin, may be very briefly stated as follows: The cells in all parts of the body are continually throwing off germinal particles, or "gemmules." The Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895

A third: It may be all caused by infinitely numerous “gemmules;” but his reason asks him: What puts infinite order into those gemmules, instead of infinite anarchy? Scientific Essays and Lectures

The organic units, during each stage of development, throw off gemmules, which, multiplying, are transmitted to the offspring. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

Pavement layer Adherent gemmules arranged close together in a single layer at the base of a sponge. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

No creature can possess such gemmules unless it inherits them from its parents, grandparents, or its less remote ancestors. On the Genesis of Species

One cannot say what gemmules of thigh and proboscis may not have got into the neutral bees’ stomachs, if they assimilate their food sufficiently, and thus into the larva. Life and Habit

From these gemmules we have ultimately produced vibrios, ready to reproduce others by the process of transverse division for a certain time, to be themselves encysted, later on. The Harvard Classics Volume 38 Scientific Papers (Physiology, Medicine, Surgery, Geology)

In this case it may be conjectured that the gemmules of the lost part were gradually all attracted by the partially diseased surface, and thus perished. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

It is easily distinguished from all others by the fact that the birotulate spicules of the gemmule are of two quite distinct kinds, which occur together on every mature gemmule. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

The quantity of gemmules emitted from every cell is very great. On the Genesis of Species

Lastly, I assume that the gemmules in their dormant state have a mutual affinity for each other, leading to their aggregation into buds or into the sexual elements. The Variation of Animals and Plants under Domestication — Volume 2

Naudin, however, does not clearly distinguish between hybrid and pure gemmules, and makes the assumption that the hybrid or mixed essences tend constantly to dissociate into pure parental essences, and thus lead to reversion. More Letters of Charles Darwin — Volume 2

With uncrossed breeds the same result would follow, under conditions which favoured the multiplication and development of certain dormant gemmules, as when animals become feral and revert to their pristine character. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

The gemmules either lie free in the substance of the sponge or are attached to its support; sometimes they adhere together in free or attached groups. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

In other words, the gemmules from any cell can only be developed in unison with the cell preceding it in due order of succession, and whilst in a nascent state. On the Genesis of Species

But I have further to assume that the gemmules in their undeveloped state are capable of largely multiplying themselves by self-division, like independent organisms. The Variation of Animals and Plants under Domestication — Volume 2

The "gemmule" of a Halimeda contained several articulations united, ready to burst their envelope, and become attached to some basis. More Letters of Charles Darwin — Volume 1

Sexual generation differs in some important respects, chiefly, as it would appear, in an insufficient number of gemmules being aggregated within the separate sexual elements, and probably in the presence of certain primordial cells. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

Spongill� in which the gemmules are covered with a thick, apparently granular pneumatic coat. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

The gemmules, by the hypothesis of Pangenesis, are the ultimate organized components of the body, the absolute organic atoms of which each body is composed; how then can they be divisible? On the Genesis of Species

We must believe, as previously shown, that several gemmules are requisite for the development of each cell or unit. The Variation of Animals and Plants under Domestication — Volume 2

It seems to me more probable that the gemmules affect the ovaria alone. More Letters of Charles Darwin — Volume 1

I go one small step further, and assume that each cell casts off a free gemmule, which is capable of reproducing a similar cell. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

No foraminal tubule; its place sometimes taken by an open, bowl-shaped chitinous structure the base of which is in continuity with the inner chitinous coat of the gemmule. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

If it is divisible into still smaller organic wholes, as a germ-cell is, it must be made up as the germ-cell is, of subordinate component atoms, which are then the true gemmules. On the Genesis of Species

But it does not seem improbable that certain gemmules, under favourable conditions, should be retained and go on multiplying for a much longer period than others. The Variation of Animals and Plants under Domestication — Volume 2

If I ask myself how you derive, and where you place the innumerable gemmules contained within the spermatozoa formed by a male animal during its whole life, I cannot answer myself. More Letters of Charles Darwin — Volume 1

There is another point on which it is useless to speculate, namely, whether all gemmules are free and separate, or whether some are from the first united into small aggregates. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

S. lacustris is an extremely variable species, varying in the size, proportions and shape of its spicules, in its external form and in the size and structure of the gemmule. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

The emission of the gemmules takes place, or may take place in all states of the cell. On the Genesis of Species

Buds apparently include nascent cells, belonging to that stage of development at which the budding occurs, and these cells are ready to unite with the gemmules derived from the next succeeding cells. The Variation of Animals and Plants under Domestication — Volume 2

The cells thus modified, I suppose cast off in their turn modified gemmules, which again combine with other nascent cells, and so on. More Letters of Charles Darwin — Volume 1

Their development is supposed to depend on their union with other partially developed cells or gemmules which precede them in the regular course of growth. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

Specimens taken at Madras by Dr. Henderson during the rains in small ponds in the sand contained no gemmules, but these structures are very numerous in sponges examined in autumn or winter. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

We can easily conceive a being so small, that a gemmule would be to it as large as St. Paul's would be to us. On the Genesis of Species

Nor does the extreme minuteness of the gemmules, which can hardly differ much in nature from the lowest and simplest organisms, render it improbable that they should grow and multiply. The Variation of Animals and Plants under Domestication — Volume 2

This is a curious mistake; the letter in "Nature," April 27th, 1871, is by Darwin himself, and refers chiefly to the question whether gemmules may be supposed to be in the blood. More Letters of Charles Darwin — Volume 1

The existence of free gemmules is a gratuitous assumption, yet can hardly be considered as very improbable, seeing that cells have the power of multiplication through the self-division of their contents. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

Some of the gemmules are often much smaller than the others. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

So that in each individual, instead of one such peculiar power and activity dominating and controlling all the parts, you have an infinity of separate powers and activities limited to the several minute component gemmules. On the Genesis of Species

Therefore the long-continued inheritance of a part which has been removed during many generations is no real anomaly, for gemmules formerly derived from the part are multiplied and transmitted from generation to generation. The Variation of Animals and Plants under Domestication — Volume 2

I believe in zoophytes universally the gemmule produces a single polypus, which afterwards or at the same time grows with its cell or single articulation. More Letters of Charles Darwin — Volume 1

But what determines the development of the gemmules of the first-formed or primordial cell in the unimpregnated ovule, is beyond conjecture. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

The gemmules germinate towards the end of the "rains," and large masses of sponge are not formed much before December. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

This process may be repeated ad infinitum, unless we get to true organic atoms, the true gemmules, whatever they may be, and they necessarily will be incapable of any process of spontaneous fission. On the Genesis of Species

In this case and in all others the proper gemmules must combine in due order with pre-existing nascent cells, owing to their elective affinities. The Variation of Animals and Plants under Domestication — Volume 2

The passage bears also a little on the struggle between the molecules or gemmules. Life and Letters of Charles Darwin — Volume 2

To understand this process we must suppose that at a certain stage of development the gemmules are multiplied at an unusual rate, and become aggregated by mutual affinity at many centres of attraction, or buds. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

This sponge is allied to S. indica, but is distinguished among other characters by its sharp skeleton-spicules and by the fact that the gemmule is covered by two chitinous membranes instead of one. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

Next, as to certain patent and notorious facts: On the hypothesis of pangenesis, no creature can develop an organ unless it possesses the component gemmules which serve for its formation. On the Genesis of Species

I go one step further, and assume that each unit casts off free gemmules which are dispersed throughout the system, and are capable under proper conditions of being developed into similar units. The Variation of Animals and Plants under Domestication — Volume 2

The Darwinian hypothesis of Pangenesis rests on the conception that all inheritable properties are represented in the cells by small invisible particles or gemmules and that these gemmules increase by division. Darwin and Modern Science

Firstly, on the deficiency, superabundance, fusion, and transposition of gemmules, and on the redevelopment of those which have long been dormant. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

They contain comparatively few gemmules and were evidently in a vigorous condition as regards vegetative growth. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

It is remarkable that Mr. Darwin brings forward in support of gemmule fission, the observation that "Thuret has seen the zoospore of an alga divide itself, and both halves germinate." On the Genesis of Species

The gemmules derived from each part or organ must be thoroughly dispersed throughout the whole system. The Variation of Animals and Plants under Domestication — Volume 2

Darwin would have soon suggested the substitution of the nuclei for his gemmules. Darwin and Modern Science

Precisely the same view may be extended to the infinitely numerous and diversified units of which the whole body in one of the higher animals is composed; and the separated atoms are our gemmules. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

True flesh-spicules are usually absent, but more or less perfect birotulates exactly similar to those associated with the gemmules are often found free in the parenchyma. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

Moreover, these gemmules are supposed to tend to aggregate themselves, and to reproduce in certain definite relations to other gemmules. On the Genesis of Species

A more perplexing problem can hardly be proposed; but on our view we have only to suppose that certain cells become at last structurally modified; and that these throw off similarly modified gemmules. The Variation of Animals and Plants under Domestication — Volume 2

In S. sinensis the gemmules are packed together in groups at the base of the sponge, and their spicules are smooth, stout, and gradually pointed. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

These almost infinitely numerous and minute gemmules must be included in each bud, ovule, spermatozoon, and pollen-grain. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

Each gemmule surrounded more or less distinctly by a circle or several circles of flesh-spicules. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

In order that each living creature may be thus furnished, the number of such gemmules in each must be inconceivably great. On the Genesis of Species

But we have further to assume that the gemmules grow, multiply, and aggregate themselves into buds and the sexual elements; their development depending on their union with other nascent cells or units. The Variation of Animals and Plants under Domestication — Volume 2

A. Microscleres of the parenchyma similar in general structure to those or the gemmule; the latter without comb-like vertical rows of spines at the ends Spongilla, p. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

Lastly, I assume that the gemmules in their dormant state have a mutual affinity for each other, leading to their aggregation either into buds or into the sexual elements. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

Its gemmules are, however, retained in the close-meshed skeleton, which persists without change of form. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

In a highly organized and complex animal, the gemmules thrown off from each different cell or unit throughout the body must be inconceivably numerous and minute. On the Genesis of Species

The difficulty, therefore, which at first appears insurmountable, of believing in the existence of gemmules so numerous and small as they must be according to our hypothesis, has no great weight. The Variation of Animals and Plants under Domestication — Volume 2

In January the gemmules floating on the surface of the ponds form a regular scum. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

Precisely the same view may be extended to one of the higher animals; although in this case many thousand gemmules must be thrown off from the various parts of the body. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

If, however, the dried sponge remains exposed to wind and rain for more than a few months, it begins to disintegrate and its gemmules are carried away to other places. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

Mr. Darwin himself is, of course, fully aware that there must be some limit to this aggregation of gemmules. On the Genesis of Species

Such cells may be said to be fertilised by the gemmules which come next in due order of development. The Variation of Animals and Plants under Domestication — Volume 2

Their cells migrate to the extremities of the sponge, leaving a mass of gemmules in the centre, and finally perish. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

But during the adult state the gemmules of the larval tail would remain dormant, for they would not meet with pre-existing cells in a proper state of development with which to unite. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

The latter consist of single gemmules and not of a pair in one case. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

If then the hypothesis of pangenesis is well founded, that rite ought to be now absolutely or nearly superfluous from the necessarily continuous absence of certain gemmules through so many centuries and so many generations. On the Genesis of Species

I certainly should have expected that gemmules would have been present in the blood, but this is no necessary part of the hypothesis, which manifestly applies to plants and the lowest animals. The Variation of Animals and Plants under Domestication — Volume 2

The most common normal form of reproduction is by means of gemmules, which are produced in great numbers towards the end of the cold weather. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

Hence the difficulty, which at first appears insurmountable, of believing in the existence of gemmules so numerous and so small as they must be according to our hypothesis, has really little weight. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

Each gemmule is covered with a thick chitinous membrane in close contact with its wall and surrounding it completely. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

We have no means of deciding whether the ordinary wear and tear of the tissues is made good by means of gemmules, or merely by the proliferation of pre-existing cells. The Variation of Animals and Plants under Domestication — Volume 2

A large proportion of the gemmules are, however, set free and either float on the surface of the water that remains in the ponds or are dried up and carried about by the wind. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

Nevertheless, the male, before he arrives at puberty, and during the season when the species does not breed, must include the proper gemmules in a latent state. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

In young sponges, therefore, free gemmules may often be found. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

This species is closely allied to S. fragilis, from which it may be distinguished by the curious twinned arrangement of its gemmules. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

But we are far from knowing whether the gemmules of all the units are free and separate from one another, or whether some are from the first united into small aggregates. The Variation of Animals and Plants under Domestication — Volume 2

Spongill� in the gemmules of which the pneumatic layer is absent or irregularly developed, its place being sometimes taken by air-spaces between the stout chitinous membranes that cover the gemmule. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

Such cells may be said to be fertilised by the gemmules which come next in the order of development. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

In some of the gemmules before me this coat measures in thickness about 1/9 of the total diameter of the gemmule. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

The gemmule-spicules lie in the membrane or membranes parallel to the surface of the gemmule, and are often so arranged as to resemble a mosaic. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

Such cases are explained by the presence of gemmules derived from each part, and disseminated throughout the body. The Variation of Animals and Plants under Domestication — Volume 2

The gemmules themselves are usually adherent to the support of the sponge. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

According to my view, the germs or gemmules of each separate part were not originally pre-formed, but are continually produced at all ages during each generation, with some handed down from preceding generations. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

The gemmules apparently lie dormant for some little time, but incessant reproduction is carried on by means of external buds, a very rare method of reproduction among the freshwater sponges. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

The outer coat forms a kind of mantle by means of the skirts of which the gemmule is fastened to the support of the sponge. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

The units, during each stage of development, throw off gemmules, which, multiplying, are transmitted to the offspring. The Variation of Animals and Plants under Domestication — Volume 2

It is therefore necessary to assume that the gemmules of S. bombayensis had been formed between July and October. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

But gemmules differ from Mr. Spencer's physiological units, inasmuch as a certain number, or mass of them, are, as we shall see, requisite for the development of each cell or part. The Variation of Animals and Plants Under Domestication, Volume II (of 2)

In the month of November, however, C. lapidosa is in full vegetative vigour, while C. bombayensis, in absolutely identical conditions, is already reduced to a mass of gemmules, having flourished during the "rains." Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

They were taken in March and were full of gemmules. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

The chief assumption is that all the units of the body, besides having the universally admitted power of growing by self-division, throw off minute gemmules which are dispersed through the system. The Variation of Animals and Plants under Domestication — Volume 2

The sponge is small in most of the species as yet known; in some species microscleres without rotul� are associated with the gemmules. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

Vertical section of part of skeleton with gemmules in situ, � 30; also a single gemmule, � 70. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

The cells from which those of the gemmules are derived are akin in origin to those that give rise to eggs and spermatozoa. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

The gemmules germinate immediately and their contents spread out over the old skeleton, secrete a chitinous membrane and begin to build up a new sponge. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

But considering how minute the molecules are, and how many go to the formation of the smallest granule of any ordinary substance, this difficulty with respect to the gemmules is not insuperable. The Variation of Animals and Plants under Domestication — Volume 2

This species appears to be related to T. pennsylvanica, from which it differs mainly in the form of its gemmule-spicules and the structure of its gemmule. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

The skeleton of the sponge is as a rule distinctly reticulate and often hard; the skeleton-spicules are either slender or stout and sometimes change considerably in proportions and outline as they approach the gemmules. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

Some zoologists are therefore of the opinion that the development of the gemmule is an instance of parthenogenesis—that is to say of an organism arising from an egg that has not been fertilized. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

The gemmules are firmly adherent to the support of the sponge, at the base of which they are congregated in groups of four or more. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

Considering also the minuteness of the gemmules and the permeability of all organic tissues, the thorough dispersion of the gemmules is not surprising. The Variation of Animals and Plants under Domestication — Volume 2

The walls of this cage, when they are in contact with those of the cages of other gemmules, are coterminous with them. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

There is a single depressed aperture in the gemmules, as a rule situated on one of the longer sides. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

In some species, however, the greater part of the skeleton remains intact, if it is not disturbed, and retains some of the gemmules in its meshwork, where they finally germinate. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

Small spherical gemmules are present but have only a thin chitinous covering without spicules or foramen. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

The assumed elective affinity of each gemmule for that particular cell which precedes it in due order of development is supported by many analogies. The Variation of Animals and Plants under Domestication — Volume 2

To prepare gemmules for examination.—Place the gemmules dry in a watch-glass with a few drops of strong nitric acid. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

The structure of the gemmules of this species differs considerably from that in any other known species of the genus, in which these structures are usually adherent and devoid of a true pneumatic coat. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

Species that inhabit running water, for example, in some cases have heavier gemmule-spicules than those that live in stagnant water, and their gemmules are the less easily carried away by the currents of the river. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

These almost infinitely numerous and minute gemmules are contained within each bud, ovule, spermatozoon, and pollen-grain. The Variation of Animals and Plants under Domestication — Volume 2

Nor do we know why the gemmules collect to form buds in certain definite places, leading to the symmetrical growth of trees and corals. The Variation of Animals and Plants under Domestication — Volume 2

Complete abortion can be accounted for only by the hypothesis given in the last chapter, namely, the final destruction of the germs or gemmules of useless parts. The Variation of Animals and Plants under Domestication — Volume 2

Precisely the same view may be extended to the infinitely numerous and diversified units of which the whole body of one of the higher animals is composed; the separated particles being our gemmules. The Variation of Animals and Plants under Domestication — Volume 2

Zykoff found that in Europe gemmules kept for two years were still alive and able to germinate. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

The answer probably is that all the gemmules of the mutilated or amputated part are gradually attracted to the diseased surface during the reparative process, and are there destroyed by the morbid action. The Variation of Animals and Plants under Domestication — Volume 2

How far units are modified during their normal growth by absorbing peculiar nutriment from the surrounding tissues, independently of their union with gemmules of a distinct nature, is another doubtful point. The Variation of Animals and Plants under Domestication — Volume 2

With uncrossed breeds the same result follows, under conditions which favour the multiplication and development of certain dormant gemmules, as when animals become feral and revert to their pristine character. The Variation of Animals and Plants under Domestication — Volume 2

In a highly-organised animal, the gemmules thrown off from each different unit throughout the body must be inconceivably numerous and minute. The Variation of Animals and Plants under Domestication — Volume 2

Their gemmules are intermediate in structure between those of that subgenus and those of Euspongilla. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z

It has also been assumed that the development of each gemmule depends on its union with another cell or unit which has just commenced its development, and which precedes it in due order of growth. The Variation of Animals and Plants under Domestication — Volume 2

But the same cells may long continue to increase by self-division, and even become modified by absorbing peculiar nutriment, without necessarily throwing off modified gemmules. The Variation of Animals and Plants under Domestication — Volume 2

When a cell or unit is from some cause modified, the gemmules derived from it will be in like manner modified. The Variation of Animals and Plants under Domestication — Volume 2

单词	gemmule
例句	gemmule Darwin's “gemmule” theory—that hereditary instructions were thrown adrift by all cells and then floated in the blood, like a million messages in bottles—suggested that blood transfusions might transmit gemmules and thereby alter heredity. The Gene 2016-06-02T00:00:00Z Gemmules secreted by the hand carried the instructions to manufacture a new hand; gemmules dispersed by the ear transmitted the code to build a new ear. The Gene 2016-06-02T00:00:00Z Darwin imagined that the cells of all organisms produce minute particles containing hereditary information—gemmules, he called them. The Gene 2016-06-02T00:00:00Z Galton tried transfusing rabbits with the blood of other rabbits to transmit the gemmules. The Gene 2016-06-02T00:00:00Z If gemmules existed, then a mouse with a surgically excised tail should produce a mouse without a tail. The Gene 2016-06-02T00:00:00Z In 1883, with rather grim determination, the German embryologist August Weismann had performed an experiment that directly attacked Darwin's gemmule theory of heredity. The Gene 2016-06-02T00:00:00Z An atypical type of asexual reproduction is found only in freshwater sponges and occurs through the formation of gemmules. Gemmules are environmentally resistant structures produced by adult sponges wherein the typical sponge morphology is inverted. Fundamentals of Biology 2015-01-01T00:00:00Z A type of asexual reproduction found only in freshwater sponges occurs through the formation of gemmules, clusters of cells surrounded by a tough outer layer. Concepts of Biology 2013-04-25T00:00:00Z Statoblasts, hibernacula, and gemmules are alike produced asexually, but they resemble the eggs of Hydra in being provided with a hard, resistant shell, and in having the capacity to lie dormant until favourable conditions return. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z The result is then, with the worst-endowed families, that the "gemmules" or latent forces of hundreds of virtuous, or at least, not vicious, generations, lie hid in their constitutions. The Dangerous Classes of New York And Twenty Years' Work Among Them If the whole ovum, about 1⁄150 in diameter, were all gemmules, the number would be sufficient to last, at this rate, one per second for 5,600 years! Was Man Created? In freshwater sponges, gemmules may survive hostile environmental conditions like changes in temperature and serve to recolonize the habitat once environmental conditions stabilize. Fundamentals of Biology 2015-01-01T00:00:00Z These granules for the sake of distinctness may be called cell-gemmules, or, as the cellular theory is not fully established, simply gemmules. The Variation of Animals and Plants Under Domestication, Volume II (of 2) Internally the gemmule consists of a mass of cells containing food-material in what may be called a tabloid form, for it consists of minutely granular plate-like bodies. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z Combination in various degrees between these gemmules is supposed to influence their appearance or non-appearance in the offspring at various stages. Life of Charles Darwin On the contrary, in all ordinary cases of mutilation the purely atavistic elements or gemmules would be set free from any modifying influence of the non-existent or mutilated part. Are the Effects of Use and Disuse Inherited? An Examination of the View Held by Spencer and Darwin Since gemmules can withstand harsh environments, are resistant to desiccation, and remain dormant for long periods, they are an excellent means of colonization for a sessile organism. Fundamentals of Biology 2015-01-01T00:00:00Z The gemmules in each organism must be thoroughly diffused; nor does this seem improbable considering their minuteness, and the steady circulation of fluids throughout the body. The Variation of Animals and Plants Under Domestication, Volume II (of 2) The gemmules of sponges growing in lakes are sometimes deficient in spicules. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z A provisional hypothesis supplementing "Natural Selection."—Statement of the hypothesis.—Difficulty as to multitude of gemmules.—As to certain modes of reproduction.—As to formations without the requisite gemmules.—Mr. On the Genesis of Species The gemmules—as in Galton's theory of heredity and with neuter insects—might be perfectly independent of pangenesis and the normal inheritance of acquired characters. Are the Effects of Use and Disuse Inherited? An Examination of the View Held by Spencer and Darwin It is supposed that fecundation is chiefly necessary to give to the gemmules the requisite amount of nourishment to insure development. Plain Facts for Old and Young So it must be with the gemmules of plants, for with certain kinds even a minute fragment of a leaf will reproduce the whole. The Variation of Animals and Plants Under Domestication, Volume II (of 2) The gemmules with their various coverings are usually spherical in shape, but in some species they are oval or depressed in outline. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z Therefore in many of such lower organisms such a congeries of ancestral gemmules must exist in every part of their bodies, since in them every part is capable of reproducing by gemmation. On the Genesis of Species Hence, when the germs or gemmules which achieve development are either better or worse than the residue, the qualities transmitted to offspring will be of an inverse character. Are the Effects of Use and Disuse Inherited? An Examination of the View Held by Spencer and Darwin The gemmules must be very small indeed, but it may be suggested that the molecules of matter are smaller still, so this fact is no objection to the theory. Plain Facts for Old and Young On the other hand, it does not seem improbable that certain gemmules, under favourable conditions, should be retained and go on multiplying for a longer period than others. The Variation of Animals and Plants Under Domestication, Volume II (of 2) The period for which the gemmule lies dormant probably depends to some extent upon environment and to some extent on the species to which it belongs. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z The gemmules possess two sorts of affinity, one of which might be called propagative, and the other germinative affinity. On the Genesis of Species Many obvious facts compelled Darwin to suppose that vast numbers of the reproductive gemmules in an individual are not thrown off by his own cells, but are the self-multiplying progeny of ancestral gemmules. Are the Effects of Use and Disuse Inherited? An Examination of the View Held by Spencer and Darwin A third—It may be all caused by infinitely numerous p. xxviii“gemmules:” but his reason asks him—What puts infinite order into these gemmules, instead of infinite anarchy? Westminster Sermons with a Preface In a highly organised and complex animal, the gemmules thrown off from each different cell or unit throughout the body must be inconceivably numerous and minute. The Variation of Animals and Plants Under Domestication, Volume II (of 2) The gemmules are single and closely adherent at the base of the sponge. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z We have seen also that in certain cases a similar multitude of gemmules must be included also in every considerable part of the whole body of each organism, but where are we to stop? On the Genesis of Species If brain-work attracts, develops and sterilizes the best gemmules, the ultimate effect of education on the intellect of posterity may differ from its immediate effect. Are the Effects of Use and Disuse Inherited? An Examination of the View Held by Spencer and Darwin According to this, every cell of every tissue and organ of the body produces minute particles called gemmules, which partake of the characters of the cells that produce them. The Doctrine of Evolution Its Basis and Its Scope But this non-diffusion of the gemmules from bud to bud may be only apparent, depending, as we shall hereafter see, on the nature of the first-formed cells in the buds. The Variation of Animals and Plants Under Domestication, Volume II (of 2) The gemmules were noted and referred to as seeds. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z What wonder then that such an excessively complex body should divide and multiply; and what parity is there between such a body and a gemmule? On the Genesis of Species Perhaps we might retain Darwin's self-multiplying gemmules without supposing them to be thrown off by the cells, which will no longer be credited with two modes of multiplication. Are the Effects of Use and Disuse Inherited? An Examination of the View Held by Spencer and Darwin He argues that it is the undeveloped germs or gemmules of the fertilised ovum that form the sexual elements of the offspring, and thus heredity and atavism are explained. Alfred Russel Wallace: Letters and Reminiscences, Vol. 2 The assumed elective affinity of each gemmule for that particular cell which precedes it in the order of development is supported by many analogies. The Variation of Animals and Plants Under Domestication, Volume II (of 2) Microscleres Smaller spicules that lie free in the substance or the derma of the sponge, or are associated with the gemmule. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z For how can gemmules attach themselves to others to which they do not normally or generally succeed? On the Genesis of Species The theory of pangenesis, as propounded by Mr. Darwin, may be very briefly stated as follows: The cells in all parts of the body are continually throwing off germinal particles, or "gemmules." The Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895 A third: It may be all caused by infinitely numerous “gemmules;” but his reason asks him: What puts infinite order into those gemmules, instead of infinite anarchy? Scientific Essays and Lectures The organic units, during each stage of development, throw off gemmules, which, multiplying, are transmitted to the offspring. The Variation of Animals and Plants Under Domestication, Volume II (of 2) Pavement layer Adherent gemmules arranged close together in a single layer at the base of a sponge. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z No creature can possess such gemmules unless it inherits them from its parents, grandparents, or its less remote ancestors. On the Genesis of Species One cannot say what gemmules of thigh and proboscis may not have got into the neutral bees’ stomachs, if they assimilate their food sufficiently, and thus into the larva. Life and Habit From these gemmules we have ultimately produced vibrios, ready to reproduce others by the process of transverse division for a certain time, to be themselves encysted, later on. The Harvard Classics Volume 38 Scientific Papers (Physiology, Medicine, Surgery, Geology) In this case it may be conjectured that the gemmules of the lost part were gradually all attracted by the partially diseased surface, and thus perished. The Variation of Animals and Plants Under Domestication, Volume II (of 2) It is easily distinguished from all others by the fact that the birotulate spicules of the gemmule are of two quite distinct kinds, which occur together on every mature gemmule. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z The quantity of gemmules emitted from every cell is very great. On the Genesis of Species Lastly, I assume that the gemmules in their dormant state have a mutual affinity for each other, leading to their aggregation into buds or into the sexual elements. The Variation of Animals and Plants under Domestication — Volume 2 Naudin, however, does not clearly distinguish between hybrid and pure gemmules, and makes the assumption that the hybrid or mixed essences tend constantly to dissociate into pure parental essences, and thus lead to reversion. More Letters of Charles Darwin — Volume 2 With uncrossed breeds the same result would follow, under conditions which favoured the multiplication and development of certain dormant gemmules, as when animals become feral and revert to their pristine character. The Variation of Animals and Plants Under Domestication, Volume II (of 2) The gemmules either lie free in the substance of the sponge or are attached to its support; sometimes they adhere together in free or attached groups. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z In other words, the gemmules from any cell can only be developed in unison with the cell preceding it in due order of succession, and whilst in a nascent state. On the Genesis of Species But I have further to assume that the gemmules in their undeveloped state are capable of largely multiplying themselves by self-division, like independent organisms. The Variation of Animals and Plants under Domestication — Volume 2 The "gemmule" of a Halimeda contained several articulations united, ready to burst their envelope, and become attached to some basis. More Letters of Charles Darwin — Volume 1 Sexual generation differs in some important respects, chiefly, as it would appear, in an insufficient number of gemmules being aggregated within the separate sexual elements, and probably in the presence of certain primordial cells. The Variation of Animals and Plants Under Domestication, Volume II (of 2) Spongill� in which the gemmules are covered with a thick, apparently granular pneumatic coat. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z The gemmules, by the hypothesis of Pangenesis, are the ultimate organized components of the body, the absolute organic atoms of which each body is composed; how then can they be divisible? On the Genesis of Species We must believe, as previously shown, that several gemmules are requisite for the development of each cell or unit. The Variation of Animals and Plants under Domestication — Volume 2 It seems to me more probable that the gemmules affect the ovaria alone. More Letters of Charles Darwin — Volume 1 I go one small step further, and assume that each cell casts off a free gemmule, which is capable of reproducing a similar cell. The Variation of Animals and Plants Under Domestication, Volume II (of 2) No foraminal tubule; its place sometimes taken by an open, bowl-shaped chitinous structure the base of which is in continuity with the inner chitinous coat of the gemmule. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z If it is divisible into still smaller organic wholes, as a germ-cell is, it must be made up as the germ-cell is, of subordinate component atoms, which are then the true gemmules. On the Genesis of Species But it does not seem improbable that certain gemmules, under favourable conditions, should be retained and go on multiplying for a much longer period than others. The Variation of Animals and Plants under Domestication — Volume 2 If I ask myself how you derive, and where you place the innumerable gemmules contained within the spermatozoa formed by a male animal during its whole life, I cannot answer myself. More Letters of Charles Darwin — Volume 1 There is another point on which it is useless to speculate, namely, whether all gemmules are free and separate, or whether some are from the first united into small aggregates. The Variation of Animals and Plants Under Domestication, Volume II (of 2) S. lacustris is an extremely variable species, varying in the size, proportions and shape of its spicules, in its external form and in the size and structure of the gemmule. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z The emission of the gemmules takes place, or may take place in all states of the cell. On the Genesis of Species Buds apparently include nascent cells, belonging to that stage of development at which the budding occurs, and these cells are ready to unite with the gemmules derived from the next succeeding cells. The Variation of Animals and Plants under Domestication — Volume 2 The cells thus modified, I suppose cast off in their turn modified gemmules, which again combine with other nascent cells, and so on. More Letters of Charles Darwin — Volume 1 Their development is supposed to depend on their union with other partially developed cells or gemmules which precede them in the regular course of growth. The Variation of Animals and Plants Under Domestication, Volume II (of 2) Specimens taken at Madras by Dr. Henderson during the rains in small ponds in the sand contained no gemmules, but these structures are very numerous in sponges examined in autumn or winter. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z We can easily conceive a being so small, that a gemmule would be to it as large as St. Paul's would be to us. On the Genesis of Species Nor does the extreme minuteness of the gemmules, which can hardly differ much in nature from the lowest and simplest organisms, render it improbable that they should grow and multiply. The Variation of Animals and Plants under Domestication — Volume 2 This is a curious mistake; the letter in "Nature," April 27th, 1871, is by Darwin himself, and refers chiefly to the question whether gemmules may be supposed to be in the blood. More Letters of Charles Darwin — Volume 1 The existence of free gemmules is a gratuitous assumption, yet can hardly be considered as very improbable, seeing that cells have the power of multiplication through the self-division of their contents. The Variation of Animals and Plants Under Domestication, Volume II (of 2) Some of the gemmules are often much smaller than the others. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z So that in each individual, instead of one such peculiar power and activity dominating and controlling all the parts, you have an infinity of separate powers and activities limited to the several minute component gemmules. On the Genesis of Species Therefore the long-continued inheritance of a part which has been removed during many generations is no real anomaly, for gemmules formerly derived from the part are multiplied and transmitted from generation to generation. The Variation of Animals and Plants under Domestication — Volume 2 I believe in zoophytes universally the gemmule produces a single polypus, which afterwards or at the same time grows with its cell or single articulation. More Letters of Charles Darwin — Volume 1 But what determines the development of the gemmules of the first-formed or primordial cell in the unimpregnated ovule, is beyond conjecture. The Variation of Animals and Plants Under Domestication, Volume II (of 2) The gemmules germinate towards the end of the "rains," and large masses of sponge are not formed much before December. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z This process may be repeated ad infinitum, unless we get to true organic atoms, the true gemmules, whatever they may be, and they necessarily will be incapable of any process of spontaneous fission. On the Genesis of Species In this case and in all others the proper gemmules must combine in due order with pre-existing nascent cells, owing to their elective affinities. The Variation of Animals and Plants under Domestication — Volume 2 The passage bears also a little on the struggle between the molecules or gemmules. Life and Letters of Charles Darwin — Volume 2 To understand this process we must suppose that at a certain stage of development the gemmules are multiplied at an unusual rate, and become aggregated by mutual affinity at many centres of attraction, or buds. The Variation of Animals and Plants Under Domestication, Volume II (of 2) This sponge is allied to S. indica, but is distinguished among other characters by its sharp skeleton-spicules and by the fact that the gemmule is covered by two chitinous membranes instead of one. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z Next, as to certain patent and notorious facts: On the hypothesis of pangenesis, no creature can develop an organ unless it possesses the component gemmules which serve for its formation. On the Genesis of Species I go one step further, and assume that each unit casts off free gemmules which are dispersed throughout the system, and are capable under proper conditions of being developed into similar units. The Variation of Animals and Plants under Domestication — Volume 2 The Darwinian hypothesis of Pangenesis rests on the conception that all inheritable properties are represented in the cells by small invisible particles or gemmules and that these gemmules increase by division. Darwin and Modern Science Firstly, on the deficiency, superabundance, fusion, and transposition of gemmules, and on the redevelopment of those which have long been dormant. The Variation of Animals and Plants Under Domestication, Volume II (of 2) They contain comparatively few gemmules and were evidently in a vigorous condition as regards vegetative growth. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z It is remarkable that Mr. Darwin brings forward in support of gemmule fission, the observation that "Thuret has seen the zoospore of an alga divide itself, and both halves germinate." On the Genesis of Species The gemmules derived from each part or organ must be thoroughly dispersed throughout the whole system. The Variation of Animals and Plants under Domestication — Volume 2 Darwin would have soon suggested the substitution of the nuclei for his gemmules. Darwin and Modern Science Precisely the same view may be extended to the infinitely numerous and diversified units of which the whole body in one of the higher animals is composed; and the separated atoms are our gemmules. The Variation of Animals and Plants Under Domestication, Volume II (of 2) True flesh-spicules are usually absent, but more or less perfect birotulates exactly similar to those associated with the gemmules are often found free in the parenchyma. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z Moreover, these gemmules are supposed to tend to aggregate themselves, and to reproduce in certain definite relations to other gemmules. On the Genesis of Species A more perplexing problem can hardly be proposed; but on our view we have only to suppose that certain cells become at last structurally modified; and that these throw off similarly modified gemmules. The Variation of Animals and Plants under Domestication — Volume 2 In S. sinensis the gemmules are packed together in groups at the base of the sponge, and their spicules are smooth, stout, and gradually pointed. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z These almost infinitely numerous and minute gemmules must be included in each bud, ovule, spermatozoon, and pollen-grain. The Variation of Animals and Plants Under Domestication, Volume II (of 2) Each gemmule surrounded more or less distinctly by a circle or several circles of flesh-spicules. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z In order that each living creature may be thus furnished, the number of such gemmules in each must be inconceivably great. On the Genesis of Species But we have further to assume that the gemmules grow, multiply, and aggregate themselves into buds and the sexual elements; their development depending on their union with other nascent cells or units. The Variation of Animals and Plants under Domestication — Volume 2 A. Microscleres of the parenchyma similar in general structure to those or the gemmule; the latter without comb-like vertical rows of spines at the ends Spongilla, p. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z Lastly, I assume that the gemmules in their dormant state have a mutual affinity for each other, leading to their aggregation either into buds or into the sexual elements. The Variation of Animals and Plants Under Domestication, Volume II (of 2) Its gemmules are, however, retained in the close-meshed skeleton, which persists without change of form. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z In a highly organized and complex animal, the gemmules thrown off from each different cell or unit throughout the body must be inconceivably numerous and minute. On the Genesis of Species The difficulty, therefore, which at first appears insurmountable, of believing in the existence of gemmules so numerous and small as they must be according to our hypothesis, has no great weight. The Variation of Animals and Plants under Domestication — Volume 2 In January the gemmules floating on the surface of the ponds form a regular scum. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z Precisely the same view may be extended to one of the higher animals; although in this case many thousand gemmules must be thrown off from the various parts of the body. The Variation of Animals and Plants Under Domestication, Volume II (of 2) If, however, the dried sponge remains exposed to wind and rain for more than a few months, it begins to disintegrate and its gemmules are carried away to other places. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z Mr. Darwin himself is, of course, fully aware that there must be some limit to this aggregation of gemmules. On the Genesis of Species Such cells may be said to be fertilised by the gemmules which come next in due order of development. The Variation of Animals and Plants under Domestication — Volume 2 Their cells migrate to the extremities of the sponge, leaving a mass of gemmules in the centre, and finally perish. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z But during the adult state the gemmules of the larval tail would remain dormant, for they would not meet with pre-existing cells in a proper state of development with which to unite. The Variation of Animals and Plants Under Domestication, Volume II (of 2) The latter consist of single gemmules and not of a pair in one case. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z If then the hypothesis of pangenesis is well founded, that rite ought to be now absolutely or nearly superfluous from the necessarily continuous absence of certain gemmules through so many centuries and so many generations. On the Genesis of Species I certainly should have expected that gemmules would have been present in the blood, but this is no necessary part of the hypothesis, which manifestly applies to plants and the lowest animals. The Variation of Animals and Plants under Domestication — Volume 2 The most common normal form of reproduction is by means of gemmules, which are produced in great numbers towards the end of the cold weather. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z Hence the difficulty, which at first appears insurmountable, of believing in the existence of gemmules so numerous and so small as they must be according to our hypothesis, has really little weight. The Variation of Animals and Plants Under Domestication, Volume II (of 2) Each gemmule is covered with a thick chitinous membrane in close contact with its wall and surrounding it completely. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z A provisional hypothesis supplementing "Natural Selection."—Statement of the hypothesis.—Difficulty as to multitude of gemmules.—As to certain modes of reproduction.—As to formations without the requisite gemmules.—Mr. On the Genesis of Species We have no means of deciding whether the ordinary wear and tear of the tissues is made good by means of gemmules, or merely by the proliferation of pre-existing cells. The Variation of Animals and Plants under Domestication — Volume 2 A large proportion of the gemmules are, however, set free and either float on the surface of the water that remains in the ponds or are dried up and carried about by the wind. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z Nevertheless, the male, before he arrives at puberty, and during the season when the species does not breed, must include the proper gemmules in a latent state. The Variation of Animals and Plants Under Domestication, Volume II (of 2) In young sponges, therefore, free gemmules may often be found. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z This species is closely allied to S. fragilis, from which it may be distinguished by the curious twinned arrangement of its gemmules. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z But we are far from knowing whether the gemmules of all the units are free and separate from one another, or whether some are from the first united into small aggregates. The Variation of Animals and Plants under Domestication — Volume 2 Spongill� in the gemmules of which the pneumatic layer is absent or irregularly developed, its place being sometimes taken by air-spaces between the stout chitinous membranes that cover the gemmule. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z Such cells may be said to be fertilised by the gemmules which come next in the order of development. The Variation of Animals and Plants Under Domestication, Volume II (of 2) In some of the gemmules before me this coat measures in thickness about 1/9 of the total diameter of the gemmule. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z The gemmule-spicules lie in the membrane or membranes parallel to the surface of the gemmule, and are often so arranged as to resemble a mosaic. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z Such cases are explained by the presence of gemmules derived from each part, and disseminated throughout the body. The Variation of Animals and Plants under Domestication — Volume 2 The gemmules themselves are usually adherent to the support of the sponge. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z According to my view, the germs or gemmules of each separate part were not originally pre-formed, but are continually produced at all ages during each generation, with some handed down from preceding generations. The Variation of Animals and Plants Under Domestication, Volume II (of 2) The gemmules apparently lie dormant for some little time, but incessant reproduction is carried on by means of external buds, a very rare method of reproduction among the freshwater sponges. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z The outer coat forms a kind of mantle by means of the skirts of which the gemmule is fastened to the support of the sponge. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z The units, during each stage of development, throw off gemmules, which, multiplying, are transmitted to the offspring. The Variation of Animals and Plants under Domestication — Volume 2 It is therefore necessary to assume that the gemmules of S. bombayensis had been formed between July and October. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z But gemmules differ from Mr. Spencer's physiological units, inasmuch as a certain number, or mass of them, are, as we shall see, requisite for the development of each cell or part. The Variation of Animals and Plants Under Domestication, Volume II (of 2) In the month of November, however, C. lapidosa is in full vegetative vigour, while C. bombayensis, in absolutely identical conditions, is already reduced to a mass of gemmules, having flourished during the "rains." Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z They were taken in March and were full of gemmules. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z The chief assumption is that all the units of the body, besides having the universally admitted power of growing by self-division, throw off minute gemmules which are dispersed through the system. The Variation of Animals and Plants under Domestication — Volume 2 The sponge is small in most of the species as yet known; in some species microscleres without rotul� are associated with the gemmules. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z Vertical section of part of skeleton with gemmules in situ, � 30; also a single gemmule, � 70. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z The cells from which those of the gemmules are derived are akin in origin to those that give rise to eggs and spermatozoa. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z The gemmules germinate immediately and their contents spread out over the old skeleton, secrete a chitinous membrane and begin to build up a new sponge. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z But considering how minute the molecules are, and how many go to the formation of the smallest granule of any ordinary substance, this difficulty with respect to the gemmules is not insuperable. The Variation of Animals and Plants under Domestication — Volume 2 This species appears to be related to T. pennsylvanica, from which it differs mainly in the form of its gemmule-spicules and the structure of its gemmule. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z The skeleton of the sponge is as a rule distinctly reticulate and often hard; the skeleton-spicules are either slender or stout and sometimes change considerably in proportions and outline as they approach the gemmules. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z Some zoologists are therefore of the opinion that the development of the gemmule is an instance of parthenogenesis—that is to say of an organism arising from an egg that has not been fertilized. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z The gemmules are firmly adherent to the support of the sponge, at the base of which they are congregated in groups of four or more. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z Considering also the minuteness of the gemmules and the permeability of all organic tissues, the thorough dispersion of the gemmules is not surprising. The Variation of Animals and Plants under Domestication — Volume 2 The walls of this cage, when they are in contact with those of the cages of other gemmules, are coterminous with them. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z There is a single depressed aperture in the gemmules, as a rule situated on one of the longer sides. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z In some species, however, the greater part of the skeleton remains intact, if it is not disturbed, and retains some of the gemmules in its meshwork, where they finally germinate. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z Small spherical gemmules are present but have only a thin chitinous covering without spicules or foramen. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z The assumed elective affinity of each gemmule for that particular cell which precedes it in due order of development is supported by many analogies. The Variation of Animals and Plants under Domestication — Volume 2 To prepare gemmules for examination.—Place the gemmules dry in a watch-glass with a few drops of strong nitric acid. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z The structure of the gemmules of this species differs considerably from that in any other known species of the genus, in which these structures are usually adherent and devoid of a true pneumatic coat. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z Species that inhabit running water, for example, in some cases have heavier gemmule-spicules than those that live in stagnant water, and their gemmules are the less easily carried away by the currents of the river. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z These almost infinitely numerous and minute gemmules are contained within each bud, ovule, spermatozoon, and pollen-grain. The Variation of Animals and Plants under Domestication — Volume 2 Nor do we know why the gemmules collect to form buds in certain definite places, leading to the symmetrical growth of trees and corals. The Variation of Animals and Plants under Domestication — Volume 2 Complete abortion can be accounted for only by the hypothesis given in the last chapter, namely, the final destruction of the germs or gemmules of useless parts. The Variation of Animals and Plants under Domestication — Volume 2 Precisely the same view may be extended to the infinitely numerous and diversified units of which the whole body of one of the higher animals is composed; the separated particles being our gemmules. The Variation of Animals and Plants under Domestication — Volume 2 Zykoff found that in Europe gemmules kept for two years were still alive and able to germinate. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z The answer probably is that all the gemmules of the mutilated or amputated part are gradually attracted to the diseased surface during the reparative process, and are there destroyed by the morbid action. The Variation of Animals and Plants under Domestication — Volume 2 How far units are modified during their normal growth by absorbing peculiar nutriment from the surrounding tissues, independently of their union with gemmules of a distinct nature, is another doubtful point. The Variation of Animals and Plants under Domestication — Volume 2 With uncrossed breeds the same result follows, under conditions which favour the multiplication and development of certain dormant gemmules, as when animals become feral and revert to their pristine character. The Variation of Animals and Plants under Domestication — Volume 2 In a highly-organised animal, the gemmules thrown off from each different unit throughout the body must be inconceivably numerous and minute. The Variation of Animals and Plants under Domestication — Volume 2 Their gemmules are intermediate in structure between those of that subgenus and those of Euspongilla. Freshwater Sponges, Hydroids & Polyzoa 2011-06-25T02:00:17.833Z It has also been assumed that the development of each gemmule depends on its union with another cell or unit which has just commenced its development, and which precedes it in due order of growth. The Variation of Animals and Plants under Domestication — Volume 2 But the same cells may long continue to increase by self-division, and even become modified by absorbing peculiar nutriment, without necessarily throwing off modified gemmules. The Variation of Animals and Plants under Domestication — Volume 2 When a cell or unit is from some cause modified, the gemmules derived from it will be in like manner modified. The Variation of Animals and Plants under Domestication — Volume 2
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