The Development of the AlHgator 341 



Figures i6a-i6f. A series of transverse sections of an embryo of the 

 approximate age of the one represented in Figure i6. 

 X 20. 



Figure i6g. A sagittal section of an embryo of the age (possibly 

 slightly younger) of the one represented in Figure i6. 

 X 20. 

 17. Surface view in profile of an embryo at the time of origin of 

 the limbs. X (about) 5. 



Figures ija-ijg. A series of transverse sections of an embryo of the 

 age of the one represented in Figure 17. X 7. 



Figure 18. Surface view in profile of the head of an embryo slightly 

 larger than, though of about the same state of de- 

 velopment as, the one represented in Figure 17. Re- 

 produced here chiefly to show the gill clefts. X 

 (about) 3. 

 19. Surface view of an embryo somewhat more developed 

 than the one just described. X (about) 3. 



Figure 20. Surface view of an embryo older than the one represented 

 in Figure 19; with well-developed manus and pes. 

 X (about) 5. 



Figures 2oa-20j. A series of transverse sections of an embryo of the 

 age of the one represented in Figure 20. X 7. 



Figure 21. A photograph of a living embryo in the egg, showing the 

 allantois, yolk mass, etc. The embryo is somewhat 

 more developed than the one shown in Figure 20. 

 XI. 



22. A photograph of a still larger embryo, removed from the 



shell and freed from the fetal membranes. X (about) i . 



23. A photograph of a still more advanced embryo, in which 



the digits are quite evident and the scales are beginning 



to show. X (about) i . 

 23a. A sagittal section of an embryo of the age of the one 



represented in Figure 23; the tail has not been shown 



in this figure. X (about) 3. 

 236. A vertical section through the head of an embryo of 



about the size (perhaps slightly smaller) of the one 



shown in Figure 23. X (about) 3. 



24. A photograph of an older embryo in which the pigmen- 



tation of the scales is evident, though not shown in the 

 figure. X (about) i. 



25. A photograph of an embryo in which the pigmentation and 



the development of the body form are practically 



