LIST OF ABBREVIATIONS. 



b. c, Basal cell. 



c. Coil. 



ch., Chromatin. 



d. e., Degenerating epithelium. 

 e., Epithelium. 



g. c, Giant cell. 



m., Mitosis. 



ms., Muscles. 



n., Nucleus. 



n. e., New epithelium. 



p. c, Principal cell. 



r., Rectum. 



r. c, Round cell. 



St., Stomach. 



vac, Vacuole. 



y. g., Yellow granules. 



y. s., Yolk spherules. 



z., Detail shown in Fig. 22. 



Plate I. 



Fig. 1. X-ray photographs. Four tadpoles, sixth day after hatching. The 

 intestinal coil filled with subnitrate of bismuth. Dorsal view. 



Fig. 2. — Photograph. Seven stages in the development of the tadpole, from 

 3 weeks after hatching to 3 days after the appearance of the fore legs. 

 Ventral view. 



Figs. 3-10. — X-ray photographs. Stages in the development of the tadpole 

 alimentary tract, from about 10 days before to 2 days after the appearance of 

 the fore legs. Alcoholic material. Normal food in the alimentary tract. 

 Ventral view. 



Figs. 11-15. — X-ray photographs. Living material. Subnitrate of bismuth 

 in the alimentary tract. The same individual photographed on June 10th 

 (Fig. 11), June 14th (Fig. 12), June 15th (Fig. 13), June 16th (Fig. 14), 

 just after the appearance of the fore legs, June 16th (Fig. 15), a few hours 

 later than Fig. 14. Ventral view. 



Fig. 16. Photomicrograph. Cross-section of the posterior part of the 

 intestine of No. VII, Fig. 2. Detail (ne) shown in Fig. 44. X 165. 



Fig. 17. Photomicrograph. Cross-section of the duodenum of No. VII, Fig. 

 2. Detail shown in Fig. 45. X 165. 



