EMBRYOLOGY OF CRYPTOBRANCHUS 



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outward; a very narrow zone of clear cytoplasm persists at the 

 periphery, and a much broader zone containing only a few scat- 

 tering yolk granules surrounds the germinal vesicle. The middle 

 portion of the yolk zone is now filled with coarse yolk granules; 

 its margins consist of fine yolk particles. The germinal vesicle 

 is still centrally situated, and the arrangement of yolk zones and 





Fig. 23 Meridional section through one of the most advanced ovocytes of an 

 adult Cryptobranchus allegheniensis killed July 6. The bounding line repre- 

 sents the zona radiata. X 20. 



cytoplasm is concentric. The nucleoli are still distributed at the 

 periphery of the germinal vesicle, with only a slight tendency 

 toward concentration at the outer side. 



In the largest ovocytes of adults killed July 6 (see fig. 23), 

 the germinal vesicle occupies a position midway between the 

 center of the egg and the periphery, on the more exposed side of 

 the egg, toward the stalk of the follicle. The animal pole is thus 



