ON ANNELIDA. 
63 
which has not been remarked but in this class. There 
are, besides, some small basilary muscles, which are de- 
rived from the lateral contractile stratum, and which, accord- 
ing as they come before or behind the base of the fasciculus 
of seta3, must cany them forward, backwards, upwards, or 
downwards. 
The other parts of the appendages of the chetopoda, mobile 
in all directions, extensible and retractile to an extremely 
remarkable degree, produce all their movements only by means 
of the subcutaneous, muscular stratum, which enters into their 
composition. 
It is pretty nearly the same with the teeth or jaws. No 
peculiar muscles have been observed in them, and their move- 
ments are owing to those of that part of the subcutaneous mus- 
cular envelope in which they are implanted. 
The setae properly so called, of length and breadth so vari- 
able, that they are sometimes fine enough, and soft enough to 
be manufactured into felt, are often disposed in fasciculi. But 
they are also sometimes like a fan, and in a single rank. 
The acicula , or pointed setae, are sometimes divided in a 
tolerably fixed manner in the fasciculi, or bundles, most fre- 
quently but one or two in number ; but sometimes also more 
numerous, as in the bristling aphrodite. 
As to the hooks, they are always on a single rank, very 
much crowded one against the other, the hook being directed 
externally and forwards. The range which they thus form is 
supported on a linear nipple, not much projecting, and com- 
prized between two lips of the skin, producing, when they 
are drawn in, a sort of stigma, analogous in appearance to 
those organs in insects, but in reality much more like the 
nipples or false feet of the caterpillars, as has been well re- 
marked by M. Latreille. 
The digestive apparatus of the chetopoda, is in general 
very simple, often composed only of a simple cylindrical 
13 
