NioKERSON — Scales of Lepidosteus. 



PLATE I. 



Fig. 1 Longitudinal section of skin of young gar-pike, 145 mm. long X 140, 

 " 2. Mucin gland cells of ectoderm ; u-d, stained witii Kleinenberg's hajnia- 



toxylin ; e, stained with Boehmer's alum haematoxylin , a-d represent 



successively younger stages. X 500. 

 " 3. Longitudinal section through posterior end of very young scale from fish 



150 mm. long. X 262. 

 " 4 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. 

 " 5 Section from fish 150 mm. long, showing two stages in the formation of 



spine papillae; the section is not quite parallel to a.xis of larger 



papilla. X 370. 

 " 6. 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. 

 " 7. A longitudinal section through a spine to show the canal connecting its 



central cavity witii the exterior. X 100. 

 " 8. Odontoblast with its process extending into dentinal tubule. From lower 



surface of scale of fish 4G0 mm. long. X 500. 

 " 9. Another odontoblast, having two nuclei. Conditions as in Figure 8. 



