M. Souleyet on the Gasteropod Mollusca. 345 



the names oiPelta and Chalidis, which possess neither circulation 

 nor respiratory appendices, do likewise not present any trace of 

 these ramifications of the digestive cavity. 



2. If we study the internal structure of the branchial appen- 

 dices in all these mollusca, we see that the prolongations of the 

 digestive cavity which traverse the centre are always separated 

 from the dermoidal envelope (as is represented in the drawings of 

 M. de Quatrefages) by a layer more or less thick, according to 

 the size of these appendices, of a granulous brownish or yellowish 

 substance, which that naturalist has considered to be the liver ;• — a 

 conclusion which I completely adopt, because it seems to me 

 really impossible to give a different one. We must then admit 

 that the oxygenation of the nutritive matters would be through 

 this organ, and that nature, which in the construction of the 

 parts destined to the function of respiration has always sought to 

 bring as near as possible the external fluid with the liquid upon 

 which it has to act, would have here followed quite a contrary 

 rule. 



3. Admitting that this action of the air was still possible, not- 

 withstanding what I have just said, it would yet be necessary to 

 explain, how the nutritive fluid, after having undergone it, could 

 be carried into the different parts of the body, in animals which 

 present no trace of organs of circulation. 



4. If we are not preoccupied with the idea of finding in the 

 organization of these animals an organic combination which takes 

 the place of the apparatus of respiration and circulation, since 

 these apparatus exist according to my observations, we may give a 

 much more natural explanation of this ramified disposition of the 

 digestive tube in the Eolidina. In fact, as I have already said, 

 these ramifications terminate in the liver, and as I shall easily 

 make clear, the trunks which furnish them always open into the 

 stomachal pouch, it seems to me to follow naturally that these 

 ramified canals are biliary ducts ; thus we find them almost always 

 filled with a thick and brownish matter having all the appearance 

 of bile. This g astro-biliary apparatus (a denomination which ap- 

 pears to me more suitable than that of g astro-vascular) differs 

 from the same apparatus in most of the other mollusca only in 

 the fact that the biliary vessels, instead of uniting successively to 

 form a single trunk, form on each side a series of canals which 

 open detached in the stomachal pouch, and it is easy to detect 

 the connexion which exists between this disposition and the kind 

 of diffusion which, so to speak, the liver presents in all the ap- 

 pendices which cover the back of the animal. In another mol- 

 lusk, on the analogies of which zoologists are still very uncertain, 



Ann. <Sf Mag. N. Hist. Vol. xiv. 2 A 



