266 HILL. 
EXPLANATION OF PLATE I. 
Fic. 1. Head of Salmo fontinalis 7 mm. long, 39 days old. Ventro-cephalic 
view of the living embryo (X 27). 
Fic. 2. Left profile view of the anterior part of Salmo fontinalis, 42 days old. 
Optical section of living embryo (X 50). 
Fic. 3. Dorsal view of epiphysial vesicles in Salmo purpuratus 7.5 mm. long, 
43 days old. From the living embryo (X 50). 
Fic. 3a. Transverse optical section of epiphysial vesicles in Salmo fario, 
37 days old. Living embryo viewed in same position as Fig. 1 (X 180). 
Fic. 4. Anterior surface of transverse section through the epiphysial vesicles 
in Salmo fontinalis, 37 days old (X 180). 
Fic. 5. Anterior face of a transverse optical section of the epiphysial vesicle 
in Catostomus teres, 8 mm. long, 29 days old. Living embryo viewed in the 
same position as Fig. 1 (X 40). 
Fic. 6. Left profile view of epiphysial vesicles in Stizostedion vitreum 5 mm. 
long, Io days old. Living embryo (X 75). 
Fic. 7. Dorsal view of anterior end of living embryo. Same species and age 
as Fig. 6 (X 60). 
Fic. 8. Left profile view of epiphysial vesicles in Lepomis pallidus 2.5 mm. 
long. Living embryo (X 8o). 
Fic. 9. Left face of a section from the same series of sections as that from 
which Fig. 14 is taken. It is the fourth section to the left of the section repre- 
sented by Fig. 14. The sections are 10 uw thick (X 90). 
Fic. 10. Longitudinal section of the stalk of the epiphysis of Salmo fontinalis 
8 cm. long, one year old (X 110). 
Fic. 11. Right face of a longitudinal median section through the epiphysis 
of Salmo fontinalis, 13 mm. long, 72 days old (X 310). 
Fic. 12. From the same series of sections as that in Fig. 11, five sections to the 
left of the section represented by Fig. 11. The sections are 15 uw thick (X 310). 
Fic. 13. Frontal section through the posterior part of the dorsal wall of the 
epiphysis of same species and age as Fig. 14. The section passes along the line 
a-b of Fig. 14 (X 180). 
Fic. 14. Left face of a longitudinal median section through the epiphysis of 
Salmo purpuratus 25 mm. long, 160 days old (X 180). 
Fic. 15. Anterior face of a transverse section through the distal part of the 
epiphysis in Salmo fontinalis 8 cm. long, one year old (X 60). 
