586 SYDNEY J. HICKSON. 
through the middle of it, it would present approximately the 
outline given in the figure. 
As the ovum increases in size the trophodisc becomes more 
complicated. ‘The five primary pouches are divided longitudi- 
nally, by infoldings of the endoderm and mesoglea, into ten 
pouches, and by a similar process secondary endodermal 
pouches are formed on the inner and outer faces of some or all 
of the primary pouches. The diagrammatic figure given in 
woodcut 2 explains the formation of these pouches. It must 
not be supposed, however, that anything so clear and simple 
as this can be seen in any sections through the trophodisc. In 
thin sections through preserved specimens the pouches have 
always the appearance of having been considerably squeezed 
Woopcut 2.—Schematic vertical section through the ovum and trophodise at 
a somewhat later stage than that represented in Woodcut 1. Ov. Ovum. 
P. Primary pouch. p'. External secondary pouch. p?. Internal secondary 
pouch. ec. Primary communication between diverticulum and canal. 
and pressed together. 1am not able to assert that in fresh 
specimens this is also the case, as I have not yet had the good 
fortune to obtain any specimens alive; but when we consider 
that the ovum and trophodisc are, as arule, bounded by the 
calcareous walls of the ampulla, it is quite possible that the 
distorted appearance of the trophodisc presented by sections of 
preserved specimens is not very materially different from the 
natural appearance. 
The diagram was composed by drawing the outlines of several 
