ON ANNELIDA. 
67 
aphrodite 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 
cceca, 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 peetinarias 
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 always 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 serpulse and amphitrites, those organs situated on 
the back of the labial ring, are formed by long cirri, furnished 
with two ranks of denticulae, 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 the sabellarise, the pectinariaB, and the terebellse, 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, 
