268 HILL. 
EXPLANATION OF PLATE II. 
Fic. 15a. Left face of a median longitudinal section through the epiphysis of 
Salmo purpuratus 16 cm. long, two years old. About one-third of the epiphysial 
stalk is shown. X indicates the area represented in Fig. 16 (X 75). 
Fic. 16. A group of nerve-cells in the epiphysis of Salmo purpuratus 16 cm. 
long. From the area indicated by the letter X in Fig. 15a. 
Fic. 17. Section from the same series as Fig. 22. Four sections to the left 
of that represented by Fig. 22. The sections are 10 u thick (X go). 
Fic. 18. Left face of a longitudinal section through the posterior part of the 
roof of the prosencephalon and the anterior part of the roof of the thalamen- 
cephalon of Amia calva 15 mm. long. This section is from the same series as 
that represented by Fig. 19. Figs. 18 and 19 are so arranged as to represent a 
single longitudinal section through the roof of the prosencephalon and the 
thalamencephalon (x 75). 
Fic. 19. Left face of a median longitudinal section through the epiphysis and 
brain-roof in Amia calva 15 mm. long (X 90). 
Fic. 20. Anterior face of a transverse section through the posterior part of 
the prosencephalon of Amia calva 15 mm. long (X 50). 
Fic. 21. Anterior face of a transverse section through the epiphysial vesicles 
in Amia calva 1o.mm. long (X 180). 
Fic. 22. Right face of a longitudinal median section through the epiphysis and 
brain-roof of Amia calva Io mm. long (X 180), 
