14 MR. E. RAY LANKESTER- ON THE 
The ova and embryos were removed from the capsules for examination by cutting 
across the egg-rope. Numbers were always thus extruded on to the glass slip used, 
and a certain amount of liquid with them. A small piece of paper being placed at 
one corner to protect them from pressure, the thin cover-glass was placed over them. 
Abortive Embryos of larger Aplysia.—This is perhaps the place to mention a curious 
feature in the history of the larger Aplysia. The egg-capsules in this form contain as 
many as thirty or forty ova. They all advance in development to the condition presented 
in Plate 6. fig. 24, with well-developed rudimentary shell, velum, &c. But at this 
stage numbers of loose shells are to be found in the capsules, and the embryos are fewer 
in number. I at first thought that this was a case of casting a larval shell, as observed 
by Kroun in some Pteropods; but it soon became apparent that the embryos to which 
these shells belonged had disappeared. In some cases the embryos in a capsule were 
reduced to ten only. It is remarkable that just after this period the digestive canal 
of the embryos is fit to function—the mouth opens, and the primitive stomach-sac is 
ready to receive food. 
It seems most probable that we have here, then, a parallel to the case of certain 
Gasteropods (Purpura, Buccinum, Neritina),in which out of many true ova included in 
an ege-capsule only one develops, feeding on the others when it has attained digestive 
capacities. In this large Aplysia the destruction and appropriation of the weaker 
embryos is not consummated until they have all considerably advanced in development, 
and then a desperate struggle and subsequent cannibalism takes place. 
It is possible to suggest as an explanation of what occurred in the egg-cords of 
A. major kept by me, that abnormal conditions brought on an unhealthy condition 
leading to the death of a number of the embryos; but this does not seem to be likely, 
though it should be borne in mind as possible. 
Nothing of the kind occurred in A. minor, though kept under precisely the same con- 
ditions in the same tank with a constant stream of sea-water. This is contrary to the 
hypothesis of a diseased condition. One of the chief features of interest in the obser- 
vations which follow is the comparison which they afford of the development of two 
very closely similar species, which, notwithstanding their marked identity in adult form, 
yet exhibit very curious divergences in the details of their early development. 
Development of Aplysia major.—Plate 5. fig. 1 represents an ovum from an egg-rope 
or egg-coil, in which all were at this very early phase of development. ‘The upper part 
of the egg is seen to be coarsely granular and of a yellow tint ; the lower pole is paler 
and more transparent. The lower pole corresponds, as will be seen, to the cleayage- 
patch of Loligo, the yellow part to the residual yelk *—though here, as in most 
Mollusca Gasteropoda, there is not a complete segregation of cleavage-yelk from food- 
* March 5th, 1875.—The term “residual yelk” I made use of in a portion of this memoir relating to 
the development of the Cephalopod Zoligo. I have withdrawn the greater part of that section in order to 
incorporate observations made in the spring of 1874. In reference to the use of terms descriptive of parts of 
the yelk I may refer to my paper in Quart. Journ. Micr. Sci., April 1875. 
