ON ANNELIDA. 83 



The anterior third of the body, a little broader than the rest, 

 forms a sort of thoracic region, composed of seventeen segments: 

 they are provided on each side with a pencil of setse, above 

 and underneath, with a sort of vertical cleft, with two lips, 

 pretty similar in appearance to a long stigma, but which is really 

 produced by the re-entrance of two very crowded ranks of setce, 

 very short, and ciu'ved hook-wise. In the rest of the body, 

 composed of more than one hundred and fifty segments, there 

 are no other appendages but those ranks of hooked sette. 



The head of the terebella is but little distinct, and appears 

 as it were truncated. We may nevertheless recognize there, 

 by means of the appendages, several segments. The first, 

 or labial, which advances more or less above the mouth, in 

 the form of an epiglottis, and which supports at its upper 

 face, a variable, but often a considerable number of cirrous 

 barbies, of different lengths, and which are formed by a sort 

 of shred, bending longitudinally underneath. The second 

 ring constitutes the posterior lip ; it is much more narrow 

 above than underneath. The third supports, on each side, a 

 sort of membranaceous lobe, and forms a kind of neck. 



After the head, come the fii'st three thoracic gills; the gills 

 are in the form of arbusculag, more or less ramified, and rather 

 dorsal. The third pair is accompanied, underneath, with a 

 pencil of simple setae, but without any range of hooks. 



The mouth very large, is anterior and inferior. 



The anus is terminal, folded, and circular. 



The organs of generation (or, to speak more properly the 

 ovary), are terminated, according to Pallas, by a medial 

 orifice, situated at the edge of the first segment of the abdo- 

 minal band. 



In the organization of the terebellae, we may remark, as in 

 all the chetopods, that the sub- gelatinous epidermis, is re- 

 covered with the greatest facility, from the rest of the cuta- 

 neous envelope. The dermis is confounded with the muscular 



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