158 Prof. G. J. Allman on the Anatomy of Actzon. 
in Doris where it gives exit to a part of the hepatic secretion,—an 
office which it is by no means unlikely the branchial apertures 
in Kolis are also destined to fulfil. 
M. de Quatrefages maintains, that throughout the whole of his 
Mollusca Phlebenterata, with the exception of Kolidina, there is a 
total absence of a heart and vessels. In Holidina 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 deteon 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 Ascidia, 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 mollusk. 
It remains for us now to consider the zoological relations of 
Acteon and its true position among the Mollusca. We have seen 
that Montagu originally described able mollusk 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 Aplysie. Sander Rang, it is true, in his ‘ Manuel des 
Mollusques,’ expresses in a note his opinion that the position of 
Acteon 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 Act@on a genus in his family of 
Aplysiens. 
It is without doubt to M. de Quatrefages that we are indebted 
for having first decidedly removed Acteon from the Tecti- 
branchiate Mollusca, and placed it in the vicinity of Holis 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 Acton are truly analogous to the 
branchial papillee of Holis, their real homology bemg easily found 
