238 REPORT — 1851. 



lateral csecal appendages, an arrangement, by which, in the most perfect 

 manner, everything but the digested chyme is excluded from the caeca, ex- 

 emplifying in humble life, the principle on which the " pylorus " acts in the 

 higiier animals. The above description will serve to convey a precise con- 

 ception of the conformation of the alimentary system in the other genera of 

 Aphrodites, namely, in Polynoe (Plate X. fig. 62), Pholoe, and Sigalion, In 

 these smaller Aphrodites, the true stomach is limited to the posterior -|rds of 

 the body ; the cesophageal portion, with its embraced proboscis, engaging the 

 anterior. It is necessary to observe, that, as in Sigalion Boa, the peritoneal 

 fluid, external to, and enveloping the digestive appendages, assumes a highly 

 organized and blood-like character, having express branchial organs provided 

 for its own exposure to the aerating element. This, however, is only a modi- 

 fication, not a violation, of the principle already enounced. It should be here 

 stated, that in the AphroditacecB, the true biliary apparatus is distributed in 

 form of a dark green glandular layer over the parietes of the digestive caeca, 

 and that it is exclusively limited to these situations. 



In the genera Lumbricus and Nais (fig. 63), the digestive canal is a simple 

 segmented tube, brightly coloured yellow by the glandular biliary layer form- 

 ing one of its coats. 



In relation to the mechanism of alimentation in the suctorial Annelids, 

 which comprise the subgenera Hcemocharis, Albione, Branchellion, Clepsina, 

 and Malacobdella, the following principle may be definitively enunciated, — 

 that there exists in all species an inverse proportion, both as regards quantity 

 and quality, between the fluid contained in the peritoneal cavity and that 

 of the digestive caeca. It is accordingly found, that when the stomach 

 is reduced to the simplicity of a straight tube, unsupplied with lateral 

 caeca, the chamber of the peritoneum is spacious, and replete with a highly 

 organized fluid ; that, on the contrary, when the stomach is multiplied and 

 complicated by the addition of lateral appendages, filled with a chymous 

 fluid, the peritoneal space becomes reduced in capacity, and almost entirely 

 deprived of contents. The fluid, thus balanced, is not changed physiologically 

 when transferred from the peritoneal chamber into the interior of the digestive 

 caeca, or vice versa. Of the genus Hirudo, the following are subgenera, of 

 which the digestive system is sacculated : — the common Leech, in which 

 the sacculi are largest ; Hcemocharis, in which the hindmost pair only are 

 highly developed, the rest in front being small ; and Aulastoma nigrescens, 

 in which the whole of the anterior portion of the tube is perfectly straight, 

 having only two long caeca at the posterior extremity, on either side of the 

 rectum. 



Albione muricata presents a digestive tube perfectly devoid of all lateral 

 sacculations; this is also the case in the genus Branchellion, and that of Ma- 

 lacobdella. These Annelids are all suctorial. In some species a sucker 

 exists at both extremities, in others at the posterior only. 



NemertinidcB. — In the ' K egne Animal ' the genus Nemertes is thus cha- 

 racterized : — " C'est un ver d'une moUesse et d'un allongement extremes, lisse, 

 grele, aplati, termine a une extremite par une pointe mousse percee d'un 

 trou ; evase et largement ouvert a I'extremite opposee par ou il se fixe. 

 Son intestin traverse toute la longueur du corps. Un autre canal, probable- 

 ment relatif a la generation, serpente le long de ses parois, et finit a un 

 tubercule du bord de I'ouverture large. MM. d'Orbigny et de Blainville, 

 qui ont vu cet animal vivant, assurent que c'est I'ouverture large qui est la 

 bouche." 



" La seule espece connue (^Nemertes Borlasii, Cuv.) a plus de quatre pieds 

 de long. Elle se tient enfoncee dans le sable, et attaque, dit-on, les anomies 

 qu'elle suce dans leur coquille. Je dois ce ver singulier, dont Borlase (Corn- 



