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 
