ANNELIDES. 129 



ing at will. Besides the subulate bristles are distinguished 

 others which are thicker, straight, conical, and very sharp, in- 

 closed in a particular sheath, and generally one in each branch, 

 those of the ventral branches being commonly the strongest. 

 In some genera, however, these acicular bristles are wanting. 

 Some of the Annelides possess a third kind of bristles, which 

 M. Savigny terms hooked bristles. These are flattened and 

 armed below with sharp hooks. They are also retractile, and 

 concealed in the thickness of the skin in repose. 



The tentacular cirri are those of the first pair of feet, and 

 often those of the two or three following pairs, which are some- 

 times destitute of bristles, and have only cirri. In this case the 

 cirri acquire a greater developement, and take the appearance 

 of tentacula. The last pair of feet constitute, by an analogous 

 transformation, the two filaments which terminate the body 

 posteriorly in certain species. The first segment of the body, 

 either alone or united to some of the following ones, often 

 forms a ring larger than the others, more apparent than the 

 head j and in the last segment is a plicated anal aperture turn- 

 ed upwards. 



All the Annelides respire by branchiae, and live in water, 

 mud, sand, or moist earth. These branchiae vary much in 

 situation, size, and form. In some they are distributed along 

 the body partially or wholly, and in others they are found at 

 one extremity, chiefly the anterior. The intestine is straight, 

 generally contracted into rings, and the anus terminal. The 

 organs of circulation consist of lateral, dorsal, and central ves- 

 sels, extending the length of the body. What are termed 

 eyes in some species are but ocular points, which are not con- 

 ceived to give the faculty of sight. 



The Annelides are either naked, or construct tubes or sheaths 

 for themselves, more or less solid, in which they remain with- 

 out attachment. These tubes or sheaths are in some mem- 

 branous or horny, incrusted exteriorly with grains of sand or 

 fragments of shells, in others solid, calcareous, and homogene- 

 ous. The greater part of the Annelides are carnivorous, suck- 

 ing the blood of other animals. They are hermaphrodite, but 

 require mutual impregnation. 



Cuvier divides the class of Annelides into three orders: 1. 

 Tubicolce, those in which the branchiae are in the form of tufts at- 



VOL. II. I 



