706 JOSEPH MANGAN, 
sixth being formed of a number of open intermingling 
strands. 
The limited number of free ova examined, and the possi- 
bility of their having been subjected to abnormal conditions, 
owing to such causes as the concentration of the water in the 
aquarium, precludes a rigorous discussion of the foregoing 
facts. However, it is interesting to note that the changes 
recorded are not at all remotely paralleled in certain forms 
such as Distichopora (94) and Pennaria (’04), where 
a remarkable behaviour of the nucleus during the matura- 
tion period has been recorded. In Millepora we have, as 
in those cases, a migration of the nucleus to the periphery 
with a dissolution of the nuclear membrane, and an apparent 
casting out of chromatin into the cytoplasm until hardly any 
remains. In those forms the nucleus may lose its identity 
completely, which I have not observed in the limited speci- 
mens at my disposal. I think it possible that the maturation 
phenomena are in a like manner obscured in Millepora. The 
stage represented in figure fifteen I take to be the first 
division of the cleavage-nucleus, while figure sixteen presents 
a further stage in which several nuclear divisions have taken 
place in the as yet unsegmented ege. 
The above-mentioned anomalous behaviour of ccelenterate 
ova at maturation is discussed fully by Hickson (’94) and 
more recently by Hargitt (04, ’06). A paper by Lillie (’06) 
bearing on differentiation in the egg, normal and artificial, 
may be found of particular interest in this connection. 
Tue ZootoaicaL LABORATORY, 
THr UNIVERSITY oF MANCHESTER. 
REFERENCES. 
‘04. Hargitt, C. W.—‘“The Early Development of Pennaria 
tiarella,” ‘ Archiv f. Entw.-Mech,’ vol. xviii, 1904. 
