ENTRY OF ZOOXANTHELLZ INTO OVUM OF MILLEPORA. 701 
this period, it will be seen that the manubrium has been 
reduced to very small proportions. An enteric cavity per- 
sists, but no mouth. ‘The margins of the umbrella contain 
four or five batteries of the largest nematocysts of the 
smaller variety,and also numbers of the smallest forms. The 
swellings carrying these batteries are the reduced tentacles 
figured by Duerden (99) from living specimens in his 
aquarium. 
In the majority of cases the free ova did not differ in their 
structure from those of the last-mentioned stage (fig. 12), 
their substance being uniformly vacuolated. However, two 
specimens were exceptional, showing numerous islands of 
compact cytoplasm in the alveolar ground-mass. One of 
these contained what, I think, may be the cleavage-nucleus 
in process of division (fig. 15). Its islands were free from 
chromatin. ‘The other had some half a dozen chromatic 
bodies in as many of the islands (fig. 16), and probably 
represented, a later period in the history of the egg prior to 
segmentation. As both were of more than average diameter, 
the presence of numerous areas of compact substance sug- 
gested that an accession of material had in some way taken 
place. Perhaps, as mentioned above, this, if the case, may 
be brought about by the activity of the meluded zooxan- 
thellee. 
CONCERNING OOGENESIS. 
A. Growth of the oocyte. 
The origin of the germ-cells could not be traced out owing to 
the peculiar fact that the material containing the earlier stages 
of the female medusz always exhibited individuals which 
were at approximately the same period of their development. 
No doubt the germ-cells, as in the case of the male elements 
(91), move into the dactylozooids and gasterozooids, which 
subsequently undergo modification into meduse. However, 
they were always found in the above material, as a single, or 
