252 HILL. iver. Dx 
sary here to enter into a detailed description. The two vesicles 
lie nearly in a transverse plane, and appear to rise from a 
common median point in the posterior part of the roof of 
the primary fore-brain. The cavity of each passes into a 
common median passage which opens into the brain cavity 
below. The bulk of the anterior vesicle is less than one- 
sixth that of the posterior vesicle, and it is therefore not 
easy to find it. 
STIZOSTEDION. 
In Stizostedion vitreum, Mitch., 5 mm. long (10 days old), 
the posterior epiphysial vesicle is a small cone-shaped body 
which is attached to the posterior part of the primary fore- 
brain by a short, narrow stalk (Fig. 6). It lies in the median 
plane, with its distal end close against the epidermis of the 
head. In the living embryo I was unable to detect a cavity 
in this vesicle. 
The anterior epiphysial vesicle is an obovoid body which lies 
just in front of the posterior vesicle and a little to the left of 
the median plane (Figs. 6 and 7). Its position corresponds 
very closely to the position of the anterior epiphysial vesicle in 
Coregonus albus. Its bulk is less than one-seventh that of the 
posterior vesicle. In a left profile view it appears to lie 
between the anterior border of the posterior epiphysial vesicle 
and the brain-roof, and seems to have lost its connection with 
the latter. The pointed end is turned ventro-caudad towards 
the union of the posterior vesicle with the brain (Fig. 6). 
Because of its very small size, this vesicle is not as readily 
found as the anterior epiphysial vesicle in Salmo. 
LEPOMIS. 
In Lepomis pallidus, 2.5 mm. long (Fig. 8), the two epiphysial 
vesicles have the same position as in Stizostedion. In a dorsal 
view the anterior one lies just to the left of the median plane, 
while the posterior one occupies a median position. At this 
stage of development the anterior vesicle is connected with the 
