| 单词 | Polychaeta |
| 例句 | Saccocirrus, which also lives in sand, and more closely resembles the Polychaeta, has throughout the greater length of its body on each segment a pair of small uniramous parapodia bearing a bunch of simple setae. Encyclopaedia Britannica, 11th Edition, Volume 12, Slice 8 "Haller, Albrecht" to "Harmonium" 2012-01-02T03:00:22.443Z New Polychaeta from Beaufort, with a key to all species recorded from North Carolina. Whales, Dolphins, and Porpoises of the Western North Atlantic A Guide to Their Identification The Polychaeta, however, present us with another form of nephridium seen, for example, in Arenicola, where a large funnel leads into a short and wide excretory tube whose lumen is intercellular. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 "Cerargyrite" to "Charing Cross" Finally, there are certain Polychaeta, e g. the Capitellidae, in which the vascular system has vanished altogether, leaving a coelom containing haemoglobin-impregnated corpuscles. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 "Cerargyrite" to "Charing Cross" They are considerably reduced in number in certain Polychaeta. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 "Cerargyrite" to "Charing Cross" Among the Polychaeta the sexual worm is often more marked from the asexual form, so much so that these latter have been placed in different species or even genera. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 "Cerargyrite" to "Charing Cross" Naturally, it is among the free living forms that the parapodium is best developed, and least developed among the tubicolous Polychaeta. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 "Cerargyrite" to "Charing Cross" The Polychaeta contrast with the Oligochaeta by the great variety of outward form and by the frequency of specialization of different regions of the body. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 "Cerargyrite" to "Charing Cross" I. Nephridia.—Excretory organs which are undisputed nephridia are practically universal among the Oligochaeta, Hirudinea and Archiannelida, and occur in many Polychaeta. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 "Cerargyrite" to "Charing Cross" It has been ascertained that the nephridia of Oligochaeta are preceded in the embryo by a pair of delicate and sinuous tubes, also found in the Hirudinea and Polychaeta, which are larval excretory organs. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 "Cerargyrite" to "Charing Cross" Oligochaeta agree with the leeches and differ from most Polychaeta in that they are hermaphrodite. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 "Cerargyrite" to "Charing Cross" Coelom.—The coelom of the Hirudinea differs in most genera from that of the Oligochaeta and Polychaeta. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 "Cerargyrite" to "Charing Cross" Polychaeta.—This group may be thus defined and the definition contrasted and compared with those of the other divisions of the Chaetopoda. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 "Cerargyrite" to "Charing Cross" With a few exceptions among the Polychaeta the vascular system is always present among the Chaetopoda, and always consists of a system of vessels with definite walls, which rarely communicate with the coelom. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 "Cerargyrite" to "Charing Cross" The setae are organs of locomotion, though their large size and occasionally jagged edges in some of the Polychaeta suggest an aggressive function. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 "Cerargyrite" to "Charing Cross" Reproduction.—As is the case with the Oligochaeta, the Polychaeta furnish examples of species which multiply asexually by budding. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 "Cerargyrite" to "Charing Cross" |
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