MATURATION OF OVUM AND DEVELOPMENT OF ALLOPORA. 595 
genus, Millepora,' (2) without any trace of yolk in the ovum, 
and others, Allopora (Hickson), Distichopora (Hickson), Errina 
(Moseley), Phobothrus (Moseley), and others with abundance 
of yolk in the ovum, is in itself one of considerable interest. 
It is another example of the unequal distribution of yolk- 
bearing ova in the various orders of the animal kingdom. 
In a recent paper (2) I expressed the opinion that the pheno- 
mena observed in the early’ stages of the development of 
Millepora plicata do not justify us in assuming that the 
ovum of this species at any time in its phylogenetic history was 
charged with yolk. The early stages in the development of 
Allopora seem to me to support this view. The fact that the 
oosperm nucleus of Allopora breaks up into fragments in a 
manner comparable with, although not perfectly similar to, that 
of Millepora, without any trace of segmentation of the ovum, 
shows that the phenomena observed in the latter are not due to 
loss of food-yolk. Furthermore, if Millepora at any time in its 
philogenetic history produced yolk-bearing ova, we might expect 
to find some trace of the trophodisc, a structure that is present 
both in the male and in the female sexual organs of all the 
the other Hydrocorallines that have at present been observed ; 
but no such structure has been discovered. 
I obtained the material for these investigations from two 
sources. Professor Lankester kindly placed at my disposal 
some excellent specimens of Allopora oculina that he 
dredged in the Hardanger Fiord, and preserved partly in abso- 
lute alcohol alone and partly in absolute alcohol after treatment 
with corrosive sublimate; and to Professor Moseley I am 
indebted for some specimens of Allopora norvegica given 
to him by Mr. Murray from the Triton collection. As it is 
impossible to tell the exact age of the ova of Allopora before 
they are cut into sections, I found it necessary to make an 
immense series of preparations before I could find all the stages 
described above. The investigation has consequently taken me 
1 This statement is based upon my own researches on M. plicata. It is 
quite possible that other species of Millepora, such as M. Murrayi, may 
possess a small amount of yolk in their ova. 
