The Development of the Alligator 341 
Ficures 16a-16f. A series of transverse sections of an embryo of the 
approximate age of the one represented in Figure 16. 
X 20. 
FicurE 16g. A sagittal section of an embryo of the age (possibly 
slightly younger) of the one represented in Figure 16. 
X 20. 
17. Surface view in profile of an embryo at the time of origin of 
the limbs. (about) 5. 
Ficures 17a-17g. A series of transverse sections of an embryo of the 
age of the one represented in Figure 17. X 7. 
FicureE 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. 
FicurE 20. Surface view of an embryo older than the one represented 
in Figure 19; with well-developed manus and pes. 
X (about) 5. 
FIGURES 20a-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. 
x4. 
22. A photograph of a still larger embryo, removed from the 
shell and freed from the fetal membranes. XX (about) 1. 
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) 1. 
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. XX (about) 3. 
23b. 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 riot shown in the 
figure. XX (about) 1. 
25. A photograph of an embryo in which the pigmentation and 
the development of the body form are practically 
