No. 2.] EPIPHVSIS OF TELEOSTS AND AMTA. 255 
nuclei. Each nucleus is finely granular and has a distinct 
nucleolus. I could see no indication of the grouping of cells 
described in the epiphysis of Salmo 25 mm. long. 
On each side of the epiphysial vesicles the cavity of the 
third ventricle pushes caudad dorsal to the roof of the mid- 
brain, and ends just caudad of the epiphysis in a blind sac. 
The dorsal and mesial walls of these sacs consist of a single 
layer of cells, and extend almost toa level with the dorsal 
surface of the epiphysial vesicles, so that the latter appear to 
lie in a longitudinal median groove of the brain-roof. 
The posterior commissure makes its first appearance as a 
thickening of the brain-roof just posterior to the origin of the 
epiphysial vesicles. This thickening is due to a lengthening 
of the cells. The nuclei lie in the ventral ends of the 
elongated cells, while the dorsal portion of each cell becomes 
transparent and finely granular (Fig. 22). In the older stages 
this thickening becomes folded near its middle, and is thus 
carried ventrally into the thalamocoel (Fig. 19). 
Cephalad of the point of union of the epiphysial vesicles with 
the brain, and at a distance of .087 mm., is a transverse fold 
of the brain-roof which passes ventrally into the thalamocoel 
and separates the prosencephalon from the thalamencephalon 
(Figs. 17, 18 and 22, KX). In this manner the portion of the 
roof of the thalamencephalon just caudad to this fold has the 
appearance of being evaginated in a manner similar to that 
described in Salmo. 
Just in front of the fold that separates the prosencephalon 
from the thalamencephalon is a glove-finger-like median evag- 
ination in the brain-roof. It makes its appearance in Amia 
13 mm. long. The posterior wall of this evagination is a 
part of the fold that separates the prosencephalon from the 
thalamencephalon (Fig. 18). The anterior wall is a portion 
of the brain-roof between the two lobes of the cerebrum, while 
the lateral walls form a part of two invaginations which pass 
ventrally and laterally into the cavity of the cerebrum (Fig. 20). 
In Amia 15 mm. long this evagination becomes constricted 
near its union with the brain, and in this manner it approaches 
the form of an elongated vesicle (Figs. 18 and 20). It is 
