698 JOSHPH MANGAN. 
the cells in contact with it. The nuclei of these sister-cells 
must undergo dissolution before such a plasmodium is formed, 
for I have never observed them in the growing ovum, which, 
moreover, 1s often bordered by cells in which the nucleus is 
but faintly discernible (fig. 2). The ovum continues its 
growth, in this manner at the expense of its sister cells, until 
at or about the time of liberation of the medusz the last are 
incorporated ; and I have observed that one or two of their 
nuclei, at this stage, have in some cases persisted in the 
cytoplasm of the ege (figs. 3, 8, 9, 10). Finally the ova 
encroach upon the vacuolated substance of the manubrium 
until it is reduced to very small proportions (fig. 12), when 
they are set free. 
In the material examined it was clear that the vacuolated 
substance of the ova inthe free medusw, in all cases, contained 
numerous zooxanthelle ; but they were equally absent from 
the ova of the numerous unliberated medusex that had been 
inspected. However, after a long search some half a dozen 
medusze were found which, I think, afforded conclusive evi- 
dence that zooxanthelle pass in numbers from the manubrium 
into the ovum, and that this invasion may commence at a 
period prior to the hberation of the meduse. 
The ovum, until it has attained a considerable size, is sharply 
divided off from the vacuolated substance of the manubrium. 
Eventually a period is reached when its compact cytoplasm 
becomes continuous with the central meshwork (fig, 8). This 
stage could be commonly observed, and zooxanthellae be seen 
round the margin of the egg, but never in its compact sub- 
stance. Sometimes the egg cytoplasm displayed small inci- 
pient vacuoles. 
The subsequent period, during which vacuolisation of the 
cytoplasm of the ovum occurs, and during which the zoo- 
xanthellz are incorporated, could be found only on one piece 
of Millepora, where half a dozen meduse had reached this 
stage (fig. 9). heir ova showed a variable amount of vacuo- 
lisation, which, so far as I could make out, is in great part 
inaugurated at the inner borders of the egg substance; as 
