MATURATION OF OVUM AND DEVELOPMENT OF ALLOPORA. 585 
region of the mouth narrowed. I have found only one speci- 
men with the mouth of the diverticulum widely open. The 
pouching of the lips of the diverticulum is accompanied by an 
increase of endodermal nuclei, and it appears that there is a 
concentration of endodermal tissue in this region. In the three 
specimens that I was able to examine satisfactorily there were 
five pouches, but I am unable to assert positively that this 
number is constant in Allopora. 
In this manner, then, the first rudiments of the trophodise 
are formed. It is essentially a structure formed by the lips 
of the diverticulum for the support and nourishment of the 
ovum. 
Soon after the five pouches of the young trophodisc are 
formed small yolk-globules appear in the ovum. 
The cavities of the five pouches open into a common vesti- 
bule, which communicates, on the one hand, by a very narrow 
aperture with the diverticulum containing the ovum, and on 
the other with the canal from which these structures were 
formed. 
In woodcut 1 a diagrammatic transverse section of the 
Wooncut 1.—Schematic transverse section of a young trophodise. PP. The 
five primary pouches. 
young trophodisc is shown. Such an appearance is never seen 
in actual sections because the trophodisc is cup-shaped or 
medusa-shaped ; but if it were possible to flatten it out artifi- 
cially, and then cut an accurate transverse section exactly 
