26 
ME. E. EAT LANKESTEE ON THE 
fish’s ink-bag. It does not follow because its foundations are thus laid that its lining 
cell-layer is not derived from ingrowth of the epiblast, which is what one would look for. 
In Plate 8. fig. 27 the large cells have given rise to smaller cells more closely packed, 
and giving indications of the outlines of the coils of the alimentary canal (int), The 
wall of the detached piece of yellow yelk has become clearly defined. 
The steps of the passage to the condition of fig. 28, and from this to the phases repre- 
sented in figs. 82 & 38, are so much obscured by difficulties of observation, that I doubt 
whether it can be useful to attempt a rationale of them. 
It is sufficient to point out that in Plate 8. fig. 28 the cavities are becoming more 
clearly defined ; and whilst the embryo has increased in size, they continue to prepon- 
derate more and more over the yellow yelk-masses. 
Plate 8. fig. 29 represents the alimentary tract and surroundings of the same embryo, 
focused at a somewhat higher level. 
Plate 8. figs. 30 & 31 represent respectively the right lateral and the left lateral 
aspects of a more advanced embryo. The part marked int is now clearly enough to be 
identified as the chief gastric cavity, and its inner surface is covered with vibrating cilia. 
The part marked int' is the rectum, which turns suddenly upon the gastric chamber. 
It is this which was first sketched out by those cells which intruded themselves between 
dry and ry. The rectum is not as yet perforate. 
Plate 8. figs. 33 & 34 give a right and left lateral aspect respectively of an embryo 
of Aplysia minor at the time of quitting the egg-capsule. The whole region of the 
alimentary tract is now fully formed, though possibly there is no anal aperture at A as 
yet. The residual yelk (ry) still remains, each original yellow sphere still retaining its 
large clear nucleus, though now no longer a sphere, but rather a disk-like body. F rom 
what appears to take place in other Nudibranchs, and indeed in the Cephalopoda also, 
it is pretty certain that duct-forming outgrowths from the wall o£ the gastric cavity 
penetrate these masses, and assimilating and absorbing their substance, establish in the 
place occupied by them the molluscan liver. 
Plate 8. fig. 32. In all the views given of the later growth of the Aplysia embryo the 
oesophagus is obscured by the yellow yelk-masses which lie in the way of a lateral view ; 
but when looked at from above, as in fig. 32, and rightly focused, the whole of the first 
part of the alimentary canal may be very clearly made out as a ciliated tract running 
from the mouth to the gastric cavity marked int in the figure, and passing between the 
two yellow yelk-spheres. 
In fig. 32 the embryo is closely drawn into its shell, and the plane of focus is near 
the surface, so that the outline of the shell and the superficial extent of the yellow yelk- 
masses is given to advantage. The figure represents the embryo after its escape from 
the capsule. 
We may now pass back for a moment to note the development of the nerve- 
ganglion. As in A. major, this is seen, in Plate 8. fig. 22, making its appearance as a 
thickening of the epiblast in the velar region. In Plate 8. fig. 26 it is large and 
