64) SUPPLEMENT , 



canal, almost without enlargements, and extended from the 

 mouth to the anus ; but in some species a little more com- 

 plicated. 



The mouth is sometimes, as in the lumbrici, and neighbour- 

 ing genera, a bivalve orifice or not, situated at the anterior 

 extremity of the body ; but in a great number of cases, it is 

 no longer at the apparent extremity of the body, but rather 

 at that of two or many of its rings a little modified, and which 

 can re-enter or come forth from the part of the oesophagus 

 which corresponds to a variable number of rings which fol- 

 low. To this extensible part of the oesophagus in certain 

 chetopoda, the name of proboscis has been given, perhaps 

 erroneously; for there is no particular muscle which can serve 

 to draw it in or put it forth. It is really formed like the 

 double envelope which constitutes the rest of the body, with 

 the difference that there never are any appendages properly 

 so called, but only little accumulations of corneous tubercles, 

 the use of which is not known. Sometimes we remark, be- 

 sides, at the orifice of the first of these proboscidiform rings 

 some papillary tubercles, or even short barbies, which no 

 doubt assist the mouth in prehension. We also observe pretty 

 often in the nereides a pair of teeth or corneous hooks, curved 

 like a reaping hook, denticulated or not, on the concave edge. 

 These hooks, which have sometimes been designated under 

 the name of jaws, are in general two in number, forming a 

 lateral pair. Four have been observed in a species of nereis, 

 each occupying an angle of the extremity of the proboscidal 

 ring. Two are capable of being protruded to seize the food, 

 which is then delivered to the other to be masticated. 



These hooks are hollow in a great portion of their base, and 

 this cavity gives insertion to some muscular fibres, which, 

 without doubt, assist their movements. 



In a tolerably great number of the chetopoda, the anterior 

 part of the intestine is provided with a true buccal mass, much 



