NICKERSON — Scales of Lepidosteus. 
a 
6. 
PLATE I. 
Longitudinal section of skin of young gar-pike, 145 mm. long X 140. 
Mucin gland cells of ectoderm ; a-d, stained with Kleinenberg's hama- 
toxylin; e, stained with Boehmer’s alum hematoxylin; a-d represent 
successively younger stages. X 500. 
Longitudinal section through posterior end of very young scale from fish 
150 mm. long. X 262. 
Optical section of ectoderm, parallel with surface ; from tissue stripped 
off from surface of scales of fish 300 mm. long, after decalcifying 
the chromatophores lie at a deeper level than the gland spaces, and 
therefore appear at different focus. X 110. 
Section from fish 150 mm. long, showing two stages in the formation of 
spine papilla; the section is not quite parallel to axis of larger 
papilla. X 370. 
A part of the section next to that represented in Figure 5, showing 
summit of larger spine papilla and its peculiar shaped secreted tip 
x is line in which the farther plane of the section cuts the basement 
membrane. X 370. 
A longitudinal section through a spine to show the canal connecting its 
central cavity with the exterior. X 100. 
Odontoblast with its process extending into dentinal tubule. From lower 
surface of scale of fish 460 mm. long. X 500. 
Another odontoblast, having two nuclei. Conditions as in Figure 8. 
