424 DEVELOPMENT OF FROG AND OTHER VERTEBRATA 



The exact structure of the eggs of reptiles and the general stages 

 of reptilian development need not be considered, since both 

 resemble so closely the conditions found in birds as described in the 

 following section. The embryonic development of birds, as well 

 as their adult anatomy and fossil record, shows their close rela- 



FiG. 221. — Alligator nest and eggs. Above, the nest, chiefly composed of 

 flags, opened to show eggs. Below, external view of egg and same with shell 



opened (cf. Fig. 224 B). 



(Nest after photo, by A. M. Reese; eggs, after S F. Clarke.) 



tionship to the reptiles. In the earlier stages, at least, it would be 

 hard for anyone not an embryologist to distinguish the embryo of 

 a bird from that of a reptile, and reptilian eggs are essentially like 

 the eggs of birds save in the structure of their shells. In this con- 

 nection it may be mentioned that in one group of birds, the Megal- 

 opodes, of which the Australian brush turkey is an example, the 



