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PATTERNS AND PROBLEMS OF DEVELOPMENT 



In the unsegmcnted egg disintegration progresses basipetally from the 

 apical pole but more rapidly in a broad band over the dorsal surface to 

 the region of the gray crescent (Fig. 53, yl). In early cleavage essentially 



Fig. 53, A-D. — Differential susceptibility in early development of Rana pipiens. A, four 

 stages of disintegration in undivided egg; B, four stages in early cleavage; C, in late blastula; 

 D, in early gastrula (from Bellamy, 1919). 



the same susceptibility pattern appears (Fig. 53, B). In late cleavage a 

 region near the middle of the gray crescent begins to disintegrate at about 

 the same time as the apical pole, and the two areas spread and meet along 

 the dorsal side of the embryo (Fig. 53, C) and gradually extend basipetally 



