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 setae, must carry 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 acicul(B, 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 



