636 ERNEST WARREN. 



distinction between the individual tooth-germs becomes lost 

 dorsally (diagram 7)j but ventrally it is retained. 



Oil the euamel-cups being pinched off on separate stalks 

 ("necks'^) we should arrive at the typical condition of the 

 tooth-band seen in a reptile (diagram 8). 



EXPLANATION OF PLATE 34, 



Illustrating Dr. Ernest Warren's paper " On the Teeth of 

 Petromyzon and Myxine." 



Fig. 1, A — C. — Vertical sections of developing teeth from the margin of the 

 mouth of Petromyzon marinus (L.). X 280 diameters. 



In C the successional tooth is beginning to cornify at its apex beneath the 

 functional tooth. 



Fig. II. — -Vertical section through the median tooth of Myxine gluti- 

 nosa (L.). X 140 diameters. 



Diagram 1. — Tootii-germs budded off separately from the surface; irregu- 

 larly scattered. 

 Diagram 2. — Tooth-germs arranged in a single row. 

 Diagram 3. — Tooth-germs in contact. 

 Diagram 4. — Tooth-germs fused together to form a denial lamina {d. I.); 



)• =: dental ridge. 

 Diagrams. — Vertical section through tooth-germ of embryo Scyllium 

 catulus. B is a young tooth-germ being budded off from the pre- 

 ceding germ. 

 Diagram 6. — Three tooth-germs (1, 2, 8) and bud b. Above and below 



there are indentations marking off several germs. 

 Diagram 7. — In a somewhat older embryo the distinction between the 



individual germs tends lo disajipcar on the upper surface. 

 Diagram 8. — Enamel cups pinched off on stalks (" necks "). 



