ORIGIN OF HYPOBLAST IN PELAGIC TELEOSTEAN OVA. 29 
On the Origin of the Hypoblast in Pelagic 
Teleostean Ova. 
By 
George Brook., F.L.8. 
With Plate HI. 
In a paper which I brought before the recent meeting of 
the American Association for the Advancement of Science, 
held in Philadelphia, attention was called to certain points of 
difference in the development of pelagic and non-pelagic 
teleostean ova. After the meeting I had an opportunity of 
seeing a paper then just published by Agassiz and Whitman (1), 
and when in Cambridge Dr. Whitman very kindly showed me 
his beautiful series of drawings on this subject. The conclu- 
sions arrived at by Dr. Whitman are so completely at variance 
with my own on some points, that it appears necessary for me 
to give a detailed account of my observations with carefully 
made drawings from actual sections of the egg. I may here 
add that whereas in very small pelagic ova I have found an 
optical section of the living egg to give fairly reliable details 
of the process of segmentation, invagination, &c., I have found 
that in larger eggs this method is not to be relied on at all, 
and that a clear interpretation of the process of invagination 
can only be obtained from actual sections made from eggs 
taken at frequent intervals. 
The form which I have studied most, and from which most 
of my sections were prepared, is Trachinus vipera, a general 
account of the development of which will be found in ‘ Linn. 
