Fig. 59. Late cleavage and very early blastula stage of the salamander egg, 

 polar view. Left: In late cleavage note that the more central cells near the animal 

 pole are smaller than the outer cells at the equator. Right: In the early blastula 

 the cells are smaller than in late cleavage, but there are many more cells. 



Fig. 60. Two early stages of gastrulation in the salamander egg. Left: The 

 very beginnings of gastrulation. Some cells begin to migrate internally, and this re- 

 sults in the dark line just above center. The cells above this dark line constitute 

 the dorsal lip of the blastopore. The early gastrula is viewed from the vegetal pole. 

 Right: An early gastrula with a crescent-shaped dorsal lip. Cells are leaving the 

 surface by moving over the dorsal lip into the interior, where they form the walls 

 of the archenteron. (Courtesy Professor John A. Moore, Columbia University.) 



