A.\S C;F LMOKSTION. 345 



trie coeca varies in different species, the long posterior pair are 

 the most constant. These sucking annelides live chiefly on 

 the smaller aquatic animals which swarm around them in the 

 stagnant waters they frequent. I have taken the entire legs and 

 other parts of the common triton cristatus from the stomach 

 of the hirudo sanguisuga so abundant in our fresh water pools. 

 The intestinal canal is sacculated nearly through the whole 

 extent in the pontobdella ; but the numerous cells are here 

 more short and round than in the leech where they gene- 

 rally taper to a point. The small mouth of the halithea acu- 

 leata, furnished with two conical tentacula or antennae, opens 

 into a short membranous oesophagus, which terminates in a 

 large muscular stomach with thick firm parietes and a strong 

 coriaceous lining. The entrance of this muscular cavity is 

 furnished with four sharp, triangular, converging, horny teeth 

 analogous to those of the gastric toothed cavity of insects 

 and Crustacea ; and this sac is also analogous to the muscu- 

 lar stomach of the arenicola, lumbricus, and many other 

 annelides, and to that of the ascaris and other nematoid 

 entozoa. From this muscular gizzard, the intestine passes, 

 thin, membranous and wide, through the middle of the 

 trunk nearly in a straight course to the posterior terminal 

 orifice, giving off from the dorsal aspect of its sides, at 

 regular and short distances, long narrow cceca which send 

 out numerous branches and terminate in elongated sacs. 

 These two rows of elongated ramified coeca, coming off near 

 to each other from the dorsal side of the intestine by long 

 narrow ducts, and generally filled at their vesicular termi- 

 nations with a soft turbid brownish-coloured matter, like 

 that found in the coeca of an asterias, present a more ex- 

 tended, divided, and isolated condition, of the short coeca 

 of the leech and the simpler biliary follicles of inferior anne- 

 lides. In the halithea, which appears to subsist on a mixed 

 kind of food, like the pectinaria, form the sand and frag- 

 ments of shells commonly found in its intestine, the duo- 

 denal portion of the canal generally forms a slight redupli- 

 cation, as in that animal, by folding backwards upon itself; 

 but in the long articulated myriapodous forms of the tere- 

 bell&i amphitrites, and nereides the alimentary canal pre- 

 sents a more narrow and elongated character, and assumes 

 a zig-zag or tortuous course in its distended state, and es- 



