DR. E. B. WILSON ON THE DEVELOPMENT OF RENILLA. 735 
This fact of extremely early variation is, I believe, one of great importance. It 
is evident that a structural variation in one of the segmentation spheres must 
make itself felt, to a greater or less extent, in the structure and developrnent of 
the cells derived from it, and may therefore appear ultimately as symmetrical or 
correlated variations in the larva or adult organism, 
Leptogorgia, like Renilla, is dicecious, and the eggs are fertilised in the water 
after their discharge from the parent. The eggs are slightly smaller (‘30 millim.), 
and of a rosy tint, but are otherwise quite similar to those of Renilla. They are 
discharged in the same manner through the mouths of the polyps, and at the same 
hour of the day, viz., 6 am. Unlike Renilla, the eggs are discharged in small 
numbers only, each polyp producing, so far as could be ascertained, only two or 
three ripe eggs at a time. The polyps in all parts of the colony discharge their 
eggs nearly simultaneously. 
The segmentation is closely similar to the most common mode of Renilla, but 
differs in some rather interesting particulars. Owing perhaps to the scarcity of 
material, variations in the segmentation were not observed ; but only three or four 
eggs were kept under continuous observation from the time of fertilisation. In all 
these cases the egg underwent slight changes of form about an hour before the 
beginning of segmentation, returning afterwards to an almost perfectly spherical 
form. The interval between this change of form (which is undoubtedly, as in 
Renilla, the expression of an attempt at cleavage) and the beginning of actual 
segmentation is much greater than in Renilla. 
At the first cleavage the egg divides into sixteen very distinct equal spheres, which 
soon flatten together very completely, and a strongly marked quiescent period follows, 
during which the embryo can scarcely be distinguished from the unsegmented egg. 
This continues for about twenty minutes, when the spheres again swell up and 
become very distinct but do not divide. This condition continues for several minutes 
when the spheres again flatten down, and a second resting stage occurs which is 
rather less marked than the first. 
Unluckily, I did not succeed in procuring satisfactory sections of this stage, since 
the methods of hardening employed with Renilla proved useless for Leptogorgia. 
There is every reason to believe, however, reasoning from analogy, that this swelling 
of the spheres is accompanied by a division of their substance; and this division can 
only be in a plane parallel with the surface—in other words, it must be a delamination 
cleavage. The delamination in Renilla, as we shall see, takes place when the embryo 
consists of sixteen segmentation spheres, but with considerable irregularity, and I 
have not been able to connect it certainly with any external sign of activity. In 
Leptogorgia all of the spheres appear to divide at nearly the same moment, the 
delamination being nearly as regular as in Gorgonia or Liriope. 
5 B 2 
