158 Prof. G. J. AUman on the Anatomy of Actseon. 



in Doris where it gives exit to a part of the hepatic secretion, — an 

 office which it is by no means unhkely the branchial apertures 

 in Eolis are also destined to fulfil. 



M. de Quatrefages maintains, that throughout the whole of his 

 Mollmca Phlehenterata, with the exception of Eolidina, there is a 

 total absence of a heart and vessels. In Eolidina he allows the 

 existence of a heart and arteries, but denies that of a venous sy- 

 stem. We have already seen that so far as Actceon is concerned, 

 the French anatomist is quite in error, and we have no doubt that 

 future researches will still further prove the untenableness of his 

 positions. When we consider the extreme tenuity of the venous 

 tubes in these animals, and the colourless nature of their contents, 

 we can surely place but little reliance on any statements which 

 deny their existence solely from the fact of their having escaped 

 detection. 



But after all, is a diffused condition of the venous fluid of such 

 great importance in determining the position of a molluscous 

 animal in the zoological scale ? Setting aside the Ascidice, a 

 group universally allowed to manifest a degradation of structure, 

 we know that in Aplysia a diffusion of this very kind begins to 

 show itself in the remarkably imperfect condition of the venous 

 trunks in this genus, and yet M. de Quatrefages himself would 

 hardly be rash enough to degrade from its co-ordinate Gastero- 

 pods this highly organized moUusk. 



It remains for us now to consider the zoological relations of 

 Actaon and its true position among the Mollusca. We have seen 

 that Montagu originally described ihis moUusk under the name 

 of Aplysia, and all zoologists since his time have, with the ex- 

 ception of M. de Quatrefages, agreed in placing it in the vicinity 

 of the AplysicB. Sander Rang, it is true, in his ' Manuel des 

 Mollusques,' expresses in a note his opinion that the position of 

 Actceon is in the neighbourhood of Placobranchus, a genus esta- 

 blished by Van Hasselt for a mollusk discovered by him on the 

 coast of Java; in the text however he follows the opinion of 

 other zoologists, making Actaeon a genus in his family of 

 Aplysiens. 



It is without doubt to M. de Quatrefages that we are indebted 

 for having first decidedly removed Actceon from the Tecti- 

 branchiate Mollusca, and placed it in the vicinity of Eolis and 

 its allies, — a position which is assuredly its true one, being fully 

 borne out, not only by its internal structure but by its external 

 conformation, however at variance this last may at first appear 

 with the legitimacy of the position now assigned to it. 



The lateral expansions of Actceon are truly analogous to the 

 branchial papillse of Eolis, their real homology being easily found 



