128 ANNELIDES. 



simple, orbicular, or labiated, or in the form of a maxillary pro- 

 boscis. 



The anatomical structure of the animals of this class has 

 been investigated by Cuvier, Montegre, Spix, and Savigny; 

 and the result of their observations has led to their arrangement 

 in a separate group. The animals of this group, it may be re- 

 marked, formed part of the class Vermes of Linnaeus. 



The head in those species which are provided with one is a 

 slight anterior thickening, distinct from the first segment of the 

 body, and upon which are the antennae and eyes. The antcnnce 

 are articulated filaments, sometimes short and thick, inserted 

 on the head, and of which the number never exceeds five. 

 The eyes, to the number of two or four, are also upon the head, be- 

 hind the antennae, and between them and the first segment of 

 the body. The tentacula are either inarticulated filaments on 

 the head or anterior part of the body, or papillae more or less 

 elongated into filaments at the orifice of the mouth. The pro- 

 boscis is fleshy and contractile, composed sometimes of one, 

 sometimes of two rings, inclosing the jaws ; and the jaws are 

 horny or calcareous, inclosed in the proboscis, in number at 

 least two, and sometimes to the number of seven or nine. When 

 this is the case they are in two rows, one above the other. 



The body of the Annelides is in some naked, or without 

 hairs or bristles ; in others furnished with bristles without pa- 

 pillae, or with rows of setiferous papillae. The bristles which 

 are found without papillae are not retractile, while the setiferous 

 mammillae are generally so. These papillae or mammillae are 

 fleshy sheaths, which inclose each a bundle of subulate bristles. 

 The setae traverse the papillae, and are attached to the mus- 

 cles under the skin. M. Savigny gives the name of foot to each 

 pair of setiferous papillae, and he divides each foot into two 

 branches, one superior or dorsal, and one inferior or ventral. 

 The ventral branch is the most projecting, and that best orga- 

 nized for progressive motion. At each branch are observed 

 tubular, subarticulated, generally contractile cirri, analogous to 

 antennae. These are the antennae of the body. Those of the 

 dorsal branches are generally longest. The bristles of each 

 branch, or the subulate bristles, are hard, stiff, opaque, and shine 

 with metallic lustre. They form at each branch a moveable 

 tuft, which the animal has the power of exserting or withdraw- 



