英语词汇“somite”造句的方法、技巧、例句及翻译-英语例句辞典

The mesoderm gives rise to somites and the notochord. Biology for AP Courses 2022-06-09T00:00:00Z

Block-like structures called somites form on either side of the tube, eventually differentiating into the axial skeleton, skeletal muscle, and dermis. Anatomy and Physiology 2013-06-19T00:00:00Z

Although the molecular components of the segmentation clock are highly evolutionarily conserved across vertebrates, new somites form with different rhythms in each species. The clock that controls spine development modelled in a dish 2020-03-31T04:00:00Z

Here we show that a clock-and-wavefront mechanism is unnecessary for somite formation. [Report] Somites Without a Clock 2014-02-13T19:26:09.798Z

The head of an insect carries usually four pairs of conspicuous appendages—feelers, mandibles and two pairs of maxillae, so that the presence of four primitive somites is immediately evident. Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 4 "Hero" to "Hindu Chronology" 2012-04-04T02:00:56.447Z

It is reorganized into groups of cells called somites, which develop into facial cartilage, ribs, and lungs. Biology for AP Courses 2022-06-09T00:00:00Z

By the fourth week, mesoderm tissue located on either side of the notochord thickens and separates into a repeating series of block-like tissue structures, each of which is called a somite. Anatomy and Physiology 2013-06-19T00:00:00Z

For instance, Diaz-Cuadros et al. and Matsuda et al. did not observe final stages of somite development and vertebra formation in their human culture systems. The clock that controls spine development modelled in a dish 2020-03-31T04:00:00Z

However, these somites are not subdivided into rostral and caudal halves, which is necessary for neural segmentation. [Report] Somites Without a Clock 2014-02-13T19:26:09.798Z

The number of limb-bearing somites in the insectan head is thus seen to be seven. Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 4 "Hero" to "Hindu Chronology" 2012-04-04T02:00:56.447Z

It is reorganized into groups of cells called somites, which develop into ribs, lungs, segmental muscle, and the notochord. Biology for AP Courses 2022-06-09T00:00:00Z

As the somites enlarge, each one will split into several parts. Anatomy and Physiology 2013-06-19T00:00:00Z

The result is a striped pattern of somites that forms the blueprint for the spine. The clock that controls spine development modelled in a dish 2020-03-31T04:00:00Z

Instead, the findings suggest that somite size and shape are regulated by local cell-cell interactions. [Report] Somites Without a Clock 2014-02-13T19:26:09.798Z

The brain innervates the eyes and feelers, and must be regarded as a “syncerebrum” representing the ganglia of the three foremost limb-bearing somites united with the primitive cephalic lobes. Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 4 "Hero" to "Hindu Chronology" 2012-04-04T02:00:56.447Z

Further, the gradual appearance and differentiation of the successive somites and appendages may be accelerated, so that comparatively great advances take place at a single moult. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z

Repeating, paired blocks of tissue called somites then appear along either side of notochord. Anatomy and Physiology 2013-06-19T00:00:00Z

Identify also the somites and the girdle, the mouth with its projecting lip, and the anal opening. A Guide for the Study of Animals 2011-01-18T03:00:14.913Z

The appendages of four or more additional following somites may be turned upwards towards the mouth and assist in the taking of food. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

Besides the five limb-bearing somites just enumerated, two others must now be recognized in the head. Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 4 "Hero" to "Hindu Chronology" 2012-04-04T02:00:56.447Z

External Structure: Body.—As in all Arthropoda the body consists of a series of segments or somites which may be free or more or less coalesced together. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z

As the somites grow, they split into parts, one of which is called a sclerotome. Anatomy and Physiology 2013-06-19T00:00:00Z

They are long, slender, coiled tubes, two in each somite, lying in the body cavity, one on each side of the alimentary canal. A Guide for the Study of Animals 2011-01-18T03:00:14.913Z

At most they are present on all the pedigerous somites excepting the first and the last. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

In most Collembola the spring appears to belong to the fifth abdominal somite, but Willem, by study of the muscles, has shown that it really belongs to the fourth. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

Others have regarded it as representing the fusion of a number of somites, and others again as a “median appendage” or as a pair of appendages fused. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z

Paraxial mesodermal cells adjacent to the neural tube form blocks of cells called somites. Anatomy and Physiology 2013-06-19T00:00:00Z

Note.—The central part of the tail fin is usually included as a somite. A Guide for the Study of Animals 2011-01-18T03:00:14.913Z

This gives seven somites to the Hexapod’s head, the tergites of which are fused to form a cephalic carapace or box. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

In Peripatus they occur in every somite of the body. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

In no Crustacean, however, do all the somites of the body remain distinct. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z

Skeletal muscles, excluding those of the head and limbs, develop from mesodermal somites, whereas skeletal muscle in the head and limbs develop from general mesoderm. Anatomy and Physiology 2013-06-19T00:00:00Z

Explain the fact that crayfishes are often found alive and well with a soft shell?Compare the cephalo-thorax with the abdomen as to size, shape, and flexibility.How many somites are there in the abdomen? A Guide for the Study of Animals 2011-01-18T03:00:14.913Z

According to older views the increase of the number of somites in front of the mouth would have been regarded as a case of intercalation by new somite-budding of new prae-oral somites in the series. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

On the other hand, it may well be doubted whether the pygidial or posterior carapace is primarily due to a fusion of the tergites of somites which were previously movable and well developed. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

There is every reason to believe that, in the primitive Arthropoda, the heart was tubular in form, extending the whole length of the body, and having a pair of ostia in each somite. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z

Subclass 1, Pleurostigma.—Chilopods furnished with a rich system of branching tracheal tubes, the spiracles of which are paired and open upon the pleural area of more or fewer of the somites. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics"

Study the somite shells on every side and then state what there is in their construction which determines the direction and amount of their motion. A Guide for the Study of Animals 2011-01-18T03:00:14.913Z

However strange it may seem, we have to suppose that one by one in the course of long historical evolution somites have passed forwards and the mouth has passed backwards. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

In none of them are the appendages known, but in the form of the two carapaces and the presence of free somites they are distinctly intermediate between Limulus and the Trilobitae. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

The rudiments of the first three pairs of appendages commonly appear simultaneously, and, even in forms with embryonic development, they show differences in their mode of appearance from the succeeding somites. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z

Spiracles are present upon all the leg-bearing somites except the first and last; and the legs which are short and subequal in length consist of six segments, the basal of which remains small. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics"

How are the somite shells arranged to protect the body during bending? A Guide for the Study of Animals 2011-01-18T03:00:14.913Z

A similar history must have been slowly brought about when this second mandibulate somite in its turn became agnathous and passed in front of the mouth. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

Respiratory organs tracheal, opening upon the ventral surface of the 2nd and 3rd, and sometimes also of the 4th somite of the opisthosoma. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

At successive moults the somites increase in number, new somites being added behind those already differentiated, from a formative zone in front of the telsonic region. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z

The structure of the gonopods is unknown, and the homology between the two valves and the skeletal elements of the somites in question not clearly understood. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics"

Which do you consider the most specialized, and why?Which somite of the crayfish is without appendages? A Guide for the Study of Animals 2011-01-18T03:00:14.913Z

Arthropod head is a tagma or group of somites which differ in number and in their relative position in regard to the mouth, in different classes. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

In each somite of the mesosoma is a small, free entosternite having a similar position, but below or ventral to the nerve cords, and having a smaller number of muscles attached to it. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

Frequently, however, this exoskeletal somite may be differentiated into various regions. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z

The anterior portion of each somite is only partially cut off as a subsegment. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics"

How many somites are there in a crayfish's body, if each somite bears only one pair of appendages, as many scientists believe? A Guide for the Study of Animals 2011-01-18T03:00:14.913Z

The prostomium is essentially a part or outgrowth of the first somite, and cannot be regarded as itself a somite. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

Opisthosoma without trace of appendages; its posterior somites narrowed to form a movable tail for the support of the post-anal sclerite, which has no poison glands. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

The “growing point” of the trunk is, in fact, situated in front of this region, and, when the full number of somites has been reached, the unsegmented part remaining forms the telson of the adult. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z

The only exception to this is presented by Scutigera, where the terga corresponding to the somites bearing the fifteen pairs of legs are reduced by fusion and suppression to seven. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics"

In the direct development Bateson showed that the three divisions of the coelom arise as pouches constricted off from the archenteron or primitive gut, thus resembling the development of the mesoblastic somites of Amphioxus. Encyclopaedia Britannica, 11th Edition, Volume 3, Part 1, Slice 2 "Baconthorpe" to "Bankruptcy"

I, Coelom of the first somite which carries the antennae and is in front of the mouth. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

The body and head have the two pleural regions of each somite flattened and expanded on either side of the true gut-holding body-axis. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

It is quite probable, however, that in the primitive ancestors of existing Crustacea a still smaller number of somites formed the head. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z

The anal somite is always small and limbless. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics"

The medullary folds and notochord are evident at this stage, but no mesoblastic somites are to be seen. Development of the Digestive Canal of the American Alligator

III and IV, Coelom of the third and fourth somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

Becki, Green. a, Restored thoracic limbs in transverse section of the animal; b, section across a posterior somite; c, section across one of the sub-terminal somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

For practical purposes, however, it is convenient to include the two following somites also as cephalic. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z

The ventral system consists of a double chord uniting in each of the leg-bearing segments in a ganglionic swelling which gives off four pairs of nerves to the limbs and tissues of the somite. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics"

A slightly later stage is shown in figure 2, a dorsal view of an embryo with five pairs of mesoblastic somites. Development of the Digestive Canal of the American Alligator

Diprosthomerous in the adult condition, though embryologically the appendages of somite II and the somite itself are, as here drawn, not actually in front of the mouth. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

Opisthosoma 309 composed, at least in many cases, of eleven somites, the 11th somite very small, often hidden within the both. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

The numbers appended to the somites do not correspond to the enumeration adopted in the text. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z

Chilopoda with fifteen pairs of leg-bearing somites differentiated into larger and smaller, the 1st, 3rd, 5th, 7th, 8th, 10th, 12th and 14th being large, the others small. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics"

There are here about twenty pairs of somites, though the exact number cannot be determined. Development of the Digestive Canal of the American Alligator

Coelom of the first, second, third and fourth somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

Respiratory organs in the form of tracheal tubes opening by a pair of stigmata in the 2nd and 3rd somites of the opisthosoma. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

In many cases, however, the shell-fold coalesces with some of the succeeding somites. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z

The sternal plates of all the jaw-bearing somites have disappeared, except in the case of the somite of the toxicognath, where it may be vestigial. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics"

A dorsal view of an embryo with five pairs of mesoblastic somites. Development of the Digestive Canal of the American Alligator

The fourth somite is that in which the mouth now opens, and which accordingly has its appendages converted into hemignathous mandibles. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

The small first pair of appendages is concealed from view by the carapace, 1 to 12 are the somites of the opisthosoma; 13, the post-anal spine. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

In the region of the trunk, in many cases, paired mesoblastic bands are formed, growing in length by the division of teloblastic cells at the posterior end, and becoming segmented into somites. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z

We find solid mesoblastic somites, we find primitive streak, allantois and amnion, features we have just been explaining as the consequence of an excess of yolk in the egg. Text Book of Biology, Part 1: Vertebrata

A dorsal view of an embryo with about fifteen pairs of somites. Development of the Digestive Canal of the American Alligator

IV, V, VI, The three somites following the mouth. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

Opisthosoma without post-anal sclerite and posterior caudal elongation: with frequently a pair of small lobate appendages on the sternum of the 3rd somite. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

The large number and the uniformity of the trunk somites and their appendages, and the structure of the nervous system and of the heart in Apus, are Annelidan characters which can hardly be without significance. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z

It is composed of three united somites, each of which is composed of several distinct parts. The Gutenberg Webster's Unabridged Dictionary Section T, U, V, and W

A dorsal view of an embryo with five pairs of mesoblastic somites. Development of the Digestive Canal of the American Alligator

IV, V, and VI, Coelom of the fourth, fifth and sixth somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

The Roman numerals indicate the body somites and the two figures are adjusted for comparison. ce, Cerebral arteries; sp, supra-spinal or medullary artery; c, caudal artery; l, lateral anastomotic artery of Limulus. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

Another very common modification of the primitive method of development is found in the accelerated appearance of certain somites or appendages, disturbing the regular order of development. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z

As the upper edges of two opposing somites grow together over the medullary tube from right and left, the vertebra-arch becomes closed. The Evolution of Man — Volume 1

A dorsal view of an embryo with about fifteen pairs of somites. Development of the Digestive Canal of the American Alligator

It is practically an excalated somite, having no existence in the adult. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

These plates may fuse, and yet the somites to which they belong may remain distinct, and each have its pair of appendages well developed. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

The resemblances between the Crustacea and the Annelid worms, in such characters as the structure of the nervous system and the mode of growth of the somites, can hardly be ignored. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z

Hence we shall give the name of "somites" or primitive segments to these so-called "primitive vertebrae." The Evolution of Man — Volume 1

Figure 3 is a dorsal view of the next stage to be described; about fifteen pairs of somites are present. Development of the Digestive Canal of the American Alligator

With a single pair of parapodial jaws carried by the somite which is perforated by the mouth; this is not the first somite, but the second. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

No distinct respiratory stigmata behind the sterna of the 1st and 2nd somites of the opisthosoma. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

The two somites following the mandibular or first post-oral or buccal somite carry appendages modified as maxillae. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

These pairs of "cubes" of the mesoderm are the first traces of the primitive segments or somites, the so-called "protovertebrae." The Evolution of Man — Volume 1

The remaining somites carry single-clawed walking legs, a single pair to each somite. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

We are prohibited by a general consideration of metamerism in the Arthropoda from adopting the hypothesis of intercalation of somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

The existing Arachnida, like the higher Crustacea, are “nomomeristic,” that is to say, have a fixed typical number of somites to the body. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

Their trunks open at paired stigmata placed laterally in each somite of the trunk or in alternate somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

Embryo of the amphioxus, twenty hours old, with five somites. The Evolution of Man — Volume 1

Usually the tracheae open by paired stigmata placed upon the sides of a greater or less number of the somites, but never quite regularly on alternating somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

The buccal somite, with its mandibles, is in Hexapoda, as in Crustacea, the fourth: they are tetartognathous. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

It would be possible to suppose, on the other hand, that new somites are only beginning to make their appearance here. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

The somites of the abdomen all may carry rudimentary appendages in the embryo, and some of the hinder somites may retain their appendages in a modified form in adult life. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

The articulation of the stem-zone, to which the somites owe their origin, thus proceeds briskly from front to rear, new transverse constrictions of the "protovertebral plates" forming continuously and successively. The Evolution of Man — Volume 1

Terminal telescoping of the abdominal somites and excalation may occur in the adult, reducing the obvious abdominal somites to as few as eight. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

P, Protocerebrum or foremost cerebral mass belonging to the first somite. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

In the case of Scorpio this segment is indicated in the embryo by the presence of a pair of rudimentary appendages, carried by a well-marked somite. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

The appendages of the eighth and tenth abdominal somites are modified as gonapophyses. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

Embryo of the amphioxus, twenty four hours old, with eight somites. The Evolution of Man — Volume 1

The first somite has become a prosthomere, and carries a pair of extensile antennae. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

D, Deuterocerebrum, consisting of ganglion cells belonging to the second or mandibular somite. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

This region corresponds in both cases to six somites, as indicated by the presence of six pairs of limbs. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

The third somite as well as the second develops a pair of parapodial jaws; the first somite is a prosthomere carrying jointed antennae. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

If the latter name is retained at all, it should only be used of the sclerotom—i.e., the small part of the somites from which the later vertebra does actually develop. The Evolution of Man — Volume 1

I, II, III, coelom of the first, second and third somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

A brief indication of these facts is given by saying that the Onychophora are “deuterognathous”—that is to say, that the buccal somite carrying the mandibular hemignaths is the second of the whole series. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

There is no doubt that these are parapodial or limb appendages, carrying numerous imbricated secondary processes, and therefore comparable in essential structure to the leaf-bearing plates of the second mesosomatic somite of Limulus. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

The somites have well-marked parapodia, and the second and third, as well as the first, may give rise to tentacles which are directed forward, and thus contribute to form “the head.” Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

But the mouth remains as an inpushing of the wall of the first somite. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

Such chelate rami or limb-branches are independently developed in Crustacea and in Arachnida, and are carried by somites of the body which do not correspond in position in the two groups. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

But in higher Crustacea the cephalic “tagma” is extended, and more somites are added to the fusion, and their appendages adapted as jaws of a kind. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

They have remained unenclosed and projecting on the surface of the body, as once were the appendages of the four following somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

The wings of Hexapoda are lateral expansions of the terga of the second and third thoracic somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

The present writer is of opinion that it will be found most convenient to treat this evanescent somite as something special, and not to attempt to reckon it to either the prosoma or the mesosoma. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

There are a number of other important points of structure besides those referring to the somites and appendages in which Limulus agrees with Scorpio or other Arachnida and differs from other Arthropoda. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

The Hexapoda are not known to us in their earlier or more primitive manifestations; we only know them as possessed of a definite number of somites arranged in definite numbers in three great tagmata. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

The simple identification of somite with somite in Limulus and Scorpio seemed to be threatened by this discovery. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

It is probable that we have in the metasoma of Limulus a case of the disappearance of once clearly demarcated somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

As in Limulus, so in Scorpio, this unexpected somite and its appendages disappear in the course of development. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

Owing to its position it is convenient to term the somite which is excalated in Limulus and Scorpio “the praegenital somite.” Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

Only one somite following the first post-oral or mandibular segment has its appendages modified as jaws. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of"

In fact, more or less complete “excalation” of the somite takes place. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

XIV to XVIII, The confluent or unexpressed six somites of the metasoma. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

The soft integument and limbs of the mesosoma have been removed as well as all the viscera and muscles, so that the inner surface of the terga of these somites with their entopophyses are seen. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"

单词	somite
例句	somite The mesoderm gives rise to somites and the notochord. Biology for AP Courses 2022-06-09T00:00:00Z Block-like structures called somites form on either side of the tube, eventually differentiating into the axial skeleton, skeletal muscle, and dermis. Anatomy and Physiology 2013-06-19T00:00:00Z Although the molecular components of the segmentation clock are highly evolutionarily conserved across vertebrates, new somites form with different rhythms in each species. The clock that controls spine development modelled in a dish 2020-03-31T04:00:00Z Here we show that a clock-and-wavefront mechanism is unnecessary for somite formation. [Report] Somites Without a Clock 2014-02-13T19:26:09.798Z The head of an insect carries usually four pairs of conspicuous appendages—feelers, mandibles and two pairs of maxillae, so that the presence of four primitive somites is immediately evident. Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 4 "Hero" to "Hindu Chronology" 2012-04-04T02:00:56.447Z It is reorganized into groups of cells called somites, which develop into facial cartilage, ribs, and lungs. Biology for AP Courses 2022-06-09T00:00:00Z By the fourth week, mesoderm tissue located on either side of the notochord thickens and separates into a repeating series of block-like tissue structures, each of which is called a somite. Anatomy and Physiology 2013-06-19T00:00:00Z For instance, Diaz-Cuadros et al. and Matsuda et al. did not observe final stages of somite development and vertebra formation in their human culture systems. The clock that controls spine development modelled in a dish 2020-03-31T04:00:00Z However, these somites are not subdivided into rostral and caudal halves, which is necessary for neural segmentation. [Report] Somites Without a Clock 2014-02-13T19:26:09.798Z The number of limb-bearing somites in the insectan head is thus seen to be seven. Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 4 "Hero" to "Hindu Chronology" 2012-04-04T02:00:56.447Z It is reorganized into groups of cells called somites, which develop into ribs, lungs, segmental muscle, and the notochord. Biology for AP Courses 2022-06-09T00:00:00Z As the somites enlarge, each one will split into several parts. Anatomy and Physiology 2013-06-19T00:00:00Z The result is a striped pattern of somites that forms the blueprint for the spine. The clock that controls spine development modelled in a dish 2020-03-31T04:00:00Z Instead, the findings suggest that somite size and shape are regulated by local cell-cell interactions. [Report] Somites Without a Clock 2014-02-13T19:26:09.798Z The brain innervates the eyes and feelers, and must be regarded as a “syncerebrum” representing the ganglia of the three foremost limb-bearing somites united with the primitive cephalic lobes. Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 4 "Hero" to "Hindu Chronology" 2012-04-04T02:00:56.447Z Further, the gradual appearance and differentiation of the successive somites and appendages may be accelerated, so that comparatively great advances take place at a single moult. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z Repeating, paired blocks of tissue called somites then appear along either side of notochord. Anatomy and Physiology 2013-06-19T00:00:00Z Identify also the somites and the girdle, the mouth with its projecting lip, and the anal opening. A Guide for the Study of Animals 2011-01-18T03:00:14.913Z The appendages of four or more additional following somites may be turned upwards towards the mouth and assist in the taking of food. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" Besides the five limb-bearing somites just enumerated, two others must now be recognized in the head. Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 4 "Hero" to "Hindu Chronology" 2012-04-04T02:00:56.447Z External Structure: Body.—As in all Arthropoda the body consists of a series of segments or somites which may be free or more or less coalesced together. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z As the somites grow, they split into parts, one of which is called a sclerotome. Anatomy and Physiology 2013-06-19T00:00:00Z They are long, slender, coiled tubes, two in each somite, lying in the body cavity, one on each side of the alimentary canal. A Guide for the Study of Animals 2011-01-18T03:00:14.913Z At most they are present on all the pedigerous somites excepting the first and the last. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" In most Collembola the spring appears to belong to the fifth abdominal somite, but Willem, by study of the muscles, has shown that it really belongs to the fourth. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" Others have regarded it as representing the fusion of a number of somites, and others again as a “median appendage” or as a pair of appendages fused. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z Paraxial mesodermal cells adjacent to the neural tube form blocks of cells called somites. Anatomy and Physiology 2013-06-19T00:00:00Z Note.—The central part of the tail fin is usually included as a somite. A Guide for the Study of Animals 2011-01-18T03:00:14.913Z This gives seven somites to the Hexapod’s head, the tergites of which are fused to form a cephalic carapace or box. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" In Peripatus they occur in every somite of the body. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" In no Crustacean, however, do all the somites of the body remain distinct. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z Skeletal muscles, excluding those of the head and limbs, develop from mesodermal somites, whereas skeletal muscle in the head and limbs develop from general mesoderm. Anatomy and Physiology 2013-06-19T00:00:00Z Explain the fact that crayfishes are often found alive and well with a soft shell?Compare the cephalo-thorax with the abdomen as to size, shape, and flexibility.How many somites are there in the abdomen? A Guide for the Study of Animals 2011-01-18T03:00:14.913Z According to older views the increase of the number of somites in front of the mouth would have been regarded as a case of intercalation by new somite-budding of new prae-oral somites in the series. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" On the other hand, it may well be doubted whether the pygidial or posterior carapace is primarily due to a fusion of the tergites of somites which were previously movable and well developed. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" There is every reason to believe that, in the primitive Arthropoda, the heart was tubular in form, extending the whole length of the body, and having a pair of ostia in each somite. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z Subclass 1, Pleurostigma.—Chilopods furnished with a rich system of branching tracheal tubes, the spiracles of which are paired and open upon the pleural area of more or fewer of the somites. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics" Study the somite shells on every side and then state what there is in their construction which determines the direction and amount of their motion. A Guide for the Study of Animals 2011-01-18T03:00:14.913Z However strange it may seem, we have to suppose that one by one in the course of long historical evolution somites have passed forwards and the mouth has passed backwards. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" In none of them are the appendages known, but in the form of the two carapaces and the presence of free somites they are distinctly intermediate between Limulus and the Trilobitae. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" The rudiments of the first three pairs of appendages commonly appear simultaneously, and, even in forms with embryonic development, they show differences in their mode of appearance from the succeeding somites. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z Spiracles are present upon all the leg-bearing somites except the first and last; and the legs which are short and subequal in length consist of six segments, the basal of which remains small. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics" How are the somite shells arranged to protect the body during bending? A Guide for the Study of Animals 2011-01-18T03:00:14.913Z A similar history must have been slowly brought about when this second mandibulate somite in its turn became agnathous and passed in front of the mouth. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" Respiratory organs tracheal, opening upon the ventral surface of the 2nd and 3rd, and sometimes also of the 4th somite of the opisthosoma. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" At successive moults the somites increase in number, new somites being added behind those already differentiated, from a formative zone in front of the telsonic region. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z The structure of the gonopods is unknown, and the homology between the two valves and the skeletal elements of the somites in question not clearly understood. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics" Which do you consider the most specialized, and why?Which somite of the crayfish is without appendages? A Guide for the Study of Animals 2011-01-18T03:00:14.913Z Arthropod head is a tagma or group of somites which differ in number and in their relative position in regard to the mouth, in different classes. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" In each somite of the mesosoma is a small, free entosternite having a similar position, but below or ventral to the nerve cords, and having a smaller number of muscles attached to it. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" Frequently, however, this exoskeletal somite may be differentiated into various regions. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z The anterior portion of each somite is only partially cut off as a subsegment. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics" How many somites are there in a crayfish's body, if each somite bears only one pair of appendages, as many scientists believe? A Guide for the Study of Animals 2011-01-18T03:00:14.913Z The prostomium is essentially a part or outgrowth of the first somite, and cannot be regarded as itself a somite. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" Opisthosoma without trace of appendages; its posterior somites narrowed to form a movable tail for the support of the post-anal sclerite, which has no poison glands. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" The “growing point” of the trunk is, in fact, situated in front of this region, and, when the full number of somites has been reached, the unsegmented part remaining forms the telson of the adult. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z The only exception to this is presented by Scutigera, where the terga corresponding to the somites bearing the fifteen pairs of legs are reduced by fusion and suppression to seven. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics" In the direct development Bateson showed that the three divisions of the coelom arise as pouches constricted off from the archenteron or primitive gut, thus resembling the development of the mesoblastic somites of Amphioxus. Encyclopaedia Britannica, 11th Edition, Volume 3, Part 1, Slice 2 "Baconthorpe" to "Bankruptcy" I, Coelom of the first somite which carries the antennae and is in front of the mouth. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" The body and head have the two pleural regions of each somite flattened and expanded on either side of the true gut-holding body-axis. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" It is quite probable, however, that in the primitive ancestors of existing Crustacea a still smaller number of somites formed the head. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z The anal somite is always small and limbless. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics" The medullary folds and notochord are evident at this stage, but no mesoblastic somites are to be seen. Development of the Digestive Canal of the American Alligator III and IV, Coelom of the third and fourth somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" Becki, Green. a, Restored thoracic limbs in transverse section of the animal; b, section across a posterior somite; c, section across one of the sub-terminal somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" For practical purposes, however, it is convenient to include the two following somites also as cephalic. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z The ventral system consists of a double chord uniting in each of the leg-bearing segments in a ganglionic swelling which gives off four pairs of nerves to the limbs and tissues of the somite. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics" A slightly later stage is shown in figure 2, a dorsal view of an embryo with five pairs of mesoblastic somites. Development of the Digestive Canal of the American Alligator Diprosthomerous in the adult condition, though embryologically the appendages of somite II and the somite itself are, as here drawn, not actually in front of the mouth. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" Opisthosoma 309 composed, at least in many cases, of eleven somites, the 11th somite very small, often hidden within the both. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" The numbers appended to the somites do not correspond to the enumeration adopted in the text. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z Chilopoda with fifteen pairs of leg-bearing somites differentiated into larger and smaller, the 1st, 3rd, 5th, 7th, 8th, 10th, 12th and 14th being large, the others small. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics" There are here about twenty pairs of somites, though the exact number cannot be determined. Development of the Digestive Canal of the American Alligator Coelom of the first, second, third and fourth somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" Respiratory organs in the form of tracheal tubes opening by a pair of stigmata in the 2nd and 3rd somites of the opisthosoma. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" In many cases, however, the shell-fold coalesces with some of the succeeding somites. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z The sternal plates of all the jaw-bearing somites have disappeared, except in the case of the somite of the toxicognath, where it may be vestigial. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics" A dorsal view of an embryo with five pairs of mesoblastic somites. Development of the Digestive Canal of the American Alligator The fourth somite is that in which the mouth now opens, and which accordingly has its appendages converted into hemignathous mandibles. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" The small first pair of appendages is concealed from view by the carapace, 1 to 12 are the somites of the opisthosoma; 13, the post-anal spine. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" In the region of the trunk, in many cases, paired mesoblastic bands are formed, growing in length by the division of teloblastic cells at the posterior end, and becoming segmented into somites. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z We find solid mesoblastic somites, we find primitive streak, allantois and amnion, features we have just been explaining as the consequence of an excess of yolk in the egg. Text Book of Biology, Part 1: Vertebrata A dorsal view of an embryo with about fifteen pairs of somites. Development of the Digestive Canal of the American Alligator IV, V, VI, The three somites following the mouth. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" Opisthosoma without post-anal sclerite and posterior caudal elongation: with frequently a pair of small lobate appendages on the sternum of the 3rd somite. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" The large number and the uniformity of the trunk somites and their appendages, and the structure of the nervous system and of the heart in Apus, are Annelidan characters which can hardly be without significance. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z It is composed of three united somites, each of which is composed of several distinct parts. The Gutenberg Webster's Unabridged Dictionary Section T, U, V, and W A dorsal view of an embryo with five pairs of mesoblastic somites. Development of the Digestive Canal of the American Alligator IV, V, and VI, Coelom of the fourth, fifth and sixth somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" The Roman numerals indicate the body somites and the two figures are adjusted for comparison. ce, Cerebral arteries; sp, supra-spinal or medullary artery; c, caudal artery; l, lateral anastomotic artery of Limulus. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" Another very common modification of the primitive method of development is found in the accelerated appearance of certain somites or appendages, disturbing the regular order of development. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z As the upper edges of two opposing somites grow together over the medullary tube from right and left, the vertebra-arch becomes closed. The Evolution of Man — Volume 1 A dorsal view of an embryo with about fifteen pairs of somites. Development of the Digestive Canal of the American Alligator It is practically an excalated somite, having no existence in the adult. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" These plates may fuse, and yet the somites to which they belong may remain distinct, and each have its pair of appendages well developed. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" The resemblances between the Crustacea and the Annelid worms, in such characters as the structure of the nervous system and the mode of growth of the somites, can hardly be ignored. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z Hence we shall give the name of "somites" or primitive segments to these so-called "primitive vertebrae." The Evolution of Man — Volume 1 Figure 3 is a dorsal view of the next stage to be described; about fifteen pairs of somites are present. Development of the Digestive Canal of the American Alligator With a single pair of parapodial jaws carried by the somite which is perforated by the mouth; this is not the first somite, but the second. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" No distinct respiratory stigmata behind the sterna of the 1st and 2nd somites of the opisthosoma. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" The two somites following the mandibular or first post-oral or buccal somite carry appendages modified as maxillae. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" These pairs of "cubes" of the mesoderm are the first traces of the primitive segments or somites, the so-called "protovertebrae." The Evolution of Man — Volume 1 The remaining somites carry single-clawed walking legs, a single pair to each somite. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" We are prohibited by a general consideration of metamerism in the Arthropoda from adopting the hypothesis of intercalation of somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" The existing Arachnida, like the higher Crustacea, are “nomomeristic,” that is to say, have a fixed typical number of somites to the body. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" Their trunks open at paired stigmata placed laterally in each somite of the trunk or in alternate somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" Embryo of the amphioxus, twenty hours old, with five somites. The Evolution of Man — Volume 1 Usually the tracheae open by paired stigmata placed upon the sides of a greater or less number of the somites, but never quite regularly on alternating somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" The buccal somite, with its mandibles, is in Hexapoda, as in Crustacea, the fourth: they are tetartognathous. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" It would be possible to suppose, on the other hand, that new somites are only beginning to make their appearance here. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" The somites of the abdomen all may carry rudimentary appendages in the embryo, and some of the hinder somites may retain their appendages in a modified form in adult life. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" The articulation of the stem-zone, to which the somites owe their origin, thus proceeds briskly from front to rear, new transverse constrictions of the "protovertebral plates" forming continuously and successively. The Evolution of Man — Volume 1 Terminal telescoping of the abdominal somites and excalation may occur in the adult, reducing the obvious abdominal somites to as few as eight. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" P, Protocerebrum or foremost cerebral mass belonging to the first somite. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" In the case of Scorpio this segment is indicated in the embryo by the presence of a pair of rudimentary appendages, carried by a well-marked somite. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" The appendages of the eighth and tenth abdominal somites are modified as gonapophyses. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" Embryo of the amphioxus, twenty four hours old, with eight somites. The Evolution of Man — Volume 1 The first somite has become a prosthomere, and carries a pair of extensile antennae. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" D, Deuterocerebrum, consisting of ganglion cells belonging to the second or mandibular somite. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" This region corresponds in both cases to six somites, as indicated by the presence of six pairs of limbs. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" The third somite as well as the second develops a pair of parapodial jaws; the first somite is a prosthomere carrying jointed antennae. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" If the latter name is retained at all, it should only be used of the sclerotom—i.e., the small part of the somites from which the later vertebra does actually develop. The Evolution of Man — Volume 1 I, II, III, coelom of the first, second and third somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" A brief indication of these facts is given by saying that the Onychophora are “deuterognathous”—that is to say, that the buccal somite carrying the mandibular hemignaths is the second of the whole series. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" There is no doubt that these are parapodial or limb appendages, carrying numerous imbricated secondary processes, and therefore comparable in essential structure to the leaf-bearing plates of the second mesosomatic somite of Limulus. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" The somites have well-marked parapodia, and the second and third, as well as the first, may give rise to tentacles which are directed forward, and thus contribute to form “the head.” Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" But the mouth remains as an inpushing of the wall of the first somite. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" Such chelate rami or limb-branches are independently developed in Crustacea and in Arachnida, and are carried by somites of the body which do not correspond in position in the two groups. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" But in higher Crustacea the cephalic “tagma” is extended, and more somites are added to the fusion, and their appendages adapted as jaws of a kind. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" They have remained unenclosed and projecting on the surface of the body, as once were the appendages of the four following somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" The wings of Hexapoda are lateral expansions of the terga of the second and third thoracic somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" The present writer is of opinion that it will be found most convenient to treat this evanescent somite as something special, and not to attempt to reckon it to either the prosoma or the mesosoma. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" There are a number of other important points of structure besides those referring to the somites and appendages in which Limulus agrees with Scorpio or other Arachnida and differs from other Arthropoda. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" The Hexapoda are not known to us in their earlier or more primitive manifestations; we only know them as possessed of a definite number of somites arranged in definite numbers in three great tagmata. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" The simple identification of somite with somite in Limulus and Scorpio seemed to be threatened by this discovery. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" It is probable that we have in the metasoma of Limulus a case of the disappearance of once clearly demarcated somites. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" As in Limulus, so in Scorpio, this unexpected somite and its appendages disappear in the course of development. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" Owing to its position it is convenient to term the somite which is excalated in Limulus and Scorpio “the praegenital somite.” Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" Only one somite following the first post-oral or mandibular segment has its appendages modified as jaws. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" In fact, more or less complete “excalation” of the somite takes place. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" XIV to XVIII, The confluent or unexpressed six somites of the metasoma. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" The soft integument and limbs of the mesosoma have been removed as well as all the viscera and muscles, so that the inner surface of the terga of these somites with their entopophyses are seen. Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral"
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