MR. T. H. HUXLEY ON THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA. 49 
so-called “ mantle” of the latter, is sufficient evidence to show that it cannot be 
homologous with the “ mantle” of the former. The so-called “ margins of the cloak” 
in these genera appear to me to have much more relation to the epipodium. 
Cuvier allows a mantle to Doris, but denies it to Glaiicus and Eolldia ; why, is not 
obvious. 
Leuckart defines a mantle to be “a scutellate (schildfbrmig) dnplicature of the 
outer integument extending from the neck for a varying distance backwards.” By 
this definition however the upper surface of the anterior division of a Bulla would 
be a ‘’mantle,” which it is not, since the true mantle is obviously behind separated 
from this by a deep cleft, and how would the mantle of Firola or Carinaroides answer 
the definition ? 
If the definition which I have given of the true “ mantle” be correct, we must, I 
think, hesitate for the present in conferring that name upon the dorsal shell-bearing 
integument of Chiton. May this not be homologous with the thick-edged dorsal 
surface of a Doris, in which the calcareous particles instead of being scattered are 
united into distinct plates*? 
With regard to the shells, again, at the risk of being blamed for over-refinement, I 
would suggest, that it is, to say the least, an open question, whether the shell of 
Buccinurn is (as it is commonly supposed to be) homologous with that of Helix-, that 
of Sepia with tliat of Nautilus and Ammonites ; that of the embryo Aplysia with that 
of the adult Aplysia. Grave differences of development occur in some if not in all 
of these cases'!-. 
is a difference between their “ gills ” and those of other Mollusks, which, as he justly observes, are never processes 
of the mantle, he. cit. p. 130. The argument in the text tends to show, that in this respect there is in reality 
no difference between the “ gills” of the Nudibranchiata and those of other Mollusks. On other grounds 
however I am inclined to think that Leuckaet’s distinction is a just one. The organs called gills in the 
Nudibranchiata appear to me to be in all cases what they undoubtedly are in Eolis, viz. gastro-hepatic append- 
ages. Even in Doris, where they are gill-like, they are supplied with hepatic blood only. See Hancock and 
Embleton’s admirable memoir “ On the Anatomy of Doris,” Philosophical Transactions, 1852. 
* In D’Orbigny’s genus Villiersia, allied to Doris, the calcareous tegumentary particles of the Doridee have 
united into a flat shell, hidden in the “ mantle,” which is pierced by the apertures for the tentacles and gills. 
The disposition of the calcareous particles in the Dorida is very regular, though it seems too much to assume 
with Loven that they imitate a subspiral shell (see Loten, Oken’s Isis, 1842). 
t The memoir by Dr. Gegenbaur, “ Beitriige zur Entwickelungsgeschichte der Land Gasteropoden,” which 
has just appeared in Siebold and Kolliker’s “ Zeitschrift fiir Wissenschaftliche Zoologie,” furnishes very 
powerful support to the’doubts above suggested, since it demonstrates that the shell of Clausilia, and gives 
good reason for believing that that of Helix, are developed within the substance of the mantle, following exactly 
the type of Limax. 
" The land Gasteropoda are distinguished by the peculiar mode of development of their shell, if we may draw 
conclusions for the whole group from Helix and Clausilia. The original deposition of the shell in the interior 
of the mantle (as in the LoUgidee among the Cephalopoda) is as yet an isolated fact among the land Gastero- 
poda, of which we find no indication in other Gasteropods.” 
There seems to be a very curious relation between the internal or external nature of a shell, the curvature of 
its whorls as regards a vertical plane, and the heemal or dorsal flexure of the intestine. 
Take, first, the case of a true external shell, as that of Nautilus or Argonauta, or Atlanta. Here the direction 
