ox ANTSTELTDA. 67 



ajihrodite aculeata, and which have been regarded as gills. In 

 fact, in the family of the aphrodites, and especially in the 

 principal species, A. Aculeata, the stomach, entirely mem- 

 branaceous, is furnished throughout its whole length with long 

 coeca, pedicled, or narrowed at the place of their communi- 

 cation with the intestinal cavity, and which proceed trans- 

 versely, and dilating, even into the interval of the rings. 

 Nothing similar seems to exist in any other genus. 



The rest of the intestinal canal, most frequently without 

 convolutions, and without any notable difference of diameter, 

 proceeds directly to the anus, which is constantly terminal, 

 and ordinarily very large and transverse ; but in the pectinarise 

 it is not the same, the intestine making two convolutions of the 

 length of the body before it terminates at the anus, and those 

 convolutions being united by a sort of very slender mesentery. 



The apparatus of respiration is not aUvays specially marked 

 in the chetopoda. In fact, in the final genera, it is im- 

 possible to find the modifications of the skin, proper to con- 

 stitute lungs or gills. 



When this apparatus is specially marked, it always forms 

 true exterior gills, the form and position of which are suffi- 

 ciently different. 



In the serpulae and amphitrites, those organs situated on 

 the back of the labial ring, are formed by long cirri, furnished 

 with two ranks of denticulse, very short, and supported on a 

 sort of pedicle, as it were lamellose. We find that they are 

 almost entirely composed of a very thick vessel, which, seen 

 with the microscope, appears a sort of trachea, analogous to 

 what is observed in insects, its parietes being, in fact, sup- 

 ported by transverse fibres. 



In tbe sabellarise, the pectinari^, and the terebella?, the gills 

 ramified like little shrubs, occupy the lateral portions of the 

 cephalic rings, and it really appears that these are the vessels 

 themselves, ramified, and covered by a skin extremely thin, 



F 2 



