MATURATION OF OVUM AND DEVELOPMENT OF ALLOPORA. 579 
On the Maturation of the Ovum and the Early 
Stages in the Development of Allopora. 
By 
Sydney J. Hickson, M.A.Cantab., D.Sc.Lond., Xc., 
Fellow of Downing College, Cambridge. 
With Plate XXXVIII. 
My investigations may conveniently be considered under the 
following headings : 
1. General summary of events. 
The formation and fate of the trophodisce. 
. The changes of the germinal vesicle 
The formation of the embryonic ectoderm. 
The history of the yolk. 
6. General considerations and conclusion. 
Contrary to general custom, I propose to commence with a 
summary of events. The reason for this is that the history of 
three structures growing and changing simultaneously has to 
be considered: namely, the trophodisc, the yolk, and the 
germinal vesicle; and it will be convenient to consider briefly 
the three together before proceeding to describe them separately 
in detail. 
Se oa le 
I. Summary of Events. 
1. The ova and young embryos are, so far as my experience 
goes, only found in the younger branches of the colony. The 
sperm-morule and spermatozoa are only found in the older, 
thicker branches. The youngest ova are first seen either (a) 
