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HILL. 



[Vol. V. 



short, thick, conical stalk. The vesicle is flattened dorso-ven- 

 trally, and has a triangular cavity (S). One angle of this cavity 

 points towards the brain cavity below, into which it may be 

 traced in the other sections, while the other two angles termi- 

 nate in the lateral thickened walls of the vesicle. Some of the 

 cells (R) near the middle of the thickened right lateral wall are 

 arranged radially, while the dorsal right angle of the triangular 

 lumen seems to form an arch which communicates with the 

 central area, surrounded by these radiating cells. In the left 

 half of this epiphysial vesicle there is evidence of a similar 

 structure. The roof of the brain is thinner directly beneath 



Fig. III. — Transverse section through the anterior epiphysial vesicle of Coregonus albus. 



the posterior vesicle, and on all sides of this point it becomes 

 gradually thicker. There is thus formed a cup-shaped depres- 

 sion on the dorsal surface of the brain, and in this depression 

 the conical stalk of the vesicle lies. 



Fig. III. is from the same series of sections as Fig. II. 

 Three sections intervene between it and the section shown 

 in Fig. II. The section passes through the middle of the 

 anterior epiphysial vesicle (E) and through the anterior part 

 of the posterior vesicle (E). The sections are 10 fi. thick, and 

 the arrow, as before, shows the position of the median plane 

 of the brain. 



The anterior vesicle (E') is transversely elongated ; its dorsal 



