594 SYDNEY J. HICKSON. 
egg. From the time when the embryonic ectoderm first makes 
its appearance until the embryo escapes no marked changes 
take place in the character of the yolk bodies. There is 
undoubtedly a considerable diminution in the gross amount of 
yolk, but in the oldest embryos I have seen there was always a 
large number of these bodies in the central endodermic (?) 
mass. At no stage in the history of the ovum is there any 
structure comparable to the yolk nucleus of other lecithal 
eggs. 
VI. General Considerations and Conclusion. 
Two points of special interest may be noticed in the develop- 
ment of Allopora, namely, the trophodise and the fragmentation 
of the oosperm nucleus. It is perhaps premature to discuss 
fully the suggestions they afford until we have further informa- 
tion about other Hydrocorallines. 
I have now at my disposal some excellent specimens of Dis- 
tichopora from Torres Straits, for which I am indebted to the 
generosity of Professor Haddon, and I hope to obtain before 
long some specimens of Stylaster. Ifthere are any naturalists 
possessing well-preserved specimens of any Hydrocorallines 
(including all species of Miullepora except M. plicata) who 
could spare me a few branches for my investigations I should 
be most grateful to receive them. 
When I have had the opportunity of working up this 
material I shall discuss more fully than I am able to do now 
the bearing of these investigations. So far as our knowledge 
goes, however, it seems probable that the trophodisc is not a 
reduced Medusa. The position of the ovum within the cavity 
of the structure that would be called, if it were a reduced 
Medusa, the manubrium, the number (5) of the primitive 
pouches, the absence of any structure in development com- 
parable to the ‘“ Glockenkern,” and other considerations, all 
tell against the view that the trophodisc was at any time in the 
phylogenetic history of the Hydrocorallines a free-swimming 
Medusa. 
The fact that we find in the group of the Hydrocorallines one 
