112 BERTRAM G. SMITH 



The zona radiata and the zona pellucida begin to form simul- 

 taneously, shortly before the appearance of yolk granules. In 

 the most advanced ovocytes of a 35 cm. female, these membranes 

 are well established and a narrow zone of yolk has appeared near 

 the periphery of the ovocyte (see fig. 22). 



The zona radiata arises from the peripheral cytoplasm of the 

 ovocyte. In its early stages its inner boundary is not sharply 

 defined; its staining reaction is like that of the egg cytoplasm;, 

 aside from its cross-striation its structure, like that of the egg 

 cytoplasm, is finely granular. The zona pellucida, on the other 

 hand, is formed de novo as a product of cellular activity. In the 

 ovary of a 35 cm. female its staining reaction is different from that 

 of any other structure present: with the borax-carmine Lyonsr 

 blue picric-acid mixture it becomes green, while the ground-sub- 

 stance of the foUicular, cyst and ovarian membranes stains blue. 

 Since, later, a membrane exactly resembling the zona pellucida 

 in character sometimes, though not typically, forms between the 

 cyst membrane and the follicle (see fig. 32), it seems reasonable 

 to conclude that the zona pellucida is the product of the follicle 

 rather than of the egg. 



In the most advanced ovocytes of a spent female there is usu- 

 ally an increase in the thickness of the zona pellucida, while the 

 zona radiata shows signs of degeneration — -there is a slight loss 

 in the distinctness of the radial striations. Iri adult females 

 taken in July and August, there is a further loss in the distinctness 

 of the striations of the zona radiata. In ovocytes taken just 

 before maturation, with the germinal vesicle close to the surface, 

 the zona radiata has in some cases almost lost its radial striation, 

 is decreased in thickness, and is becoming a simple cell wall to the 



egg. 



The literature on the zona pellucida and zona radiata of the 

 amphibian egg has been reviewed by Waldeyer in Hertwig's ('06) 

 Handbuch and needs no summary here. 



The ovary of a young Necturus 20 cm. long, killed August 25, 

 gives stages corresponding to those of a 35 cm. Cryptobranchus. 

 The follicular layers and mode of attachment of the ovocyte to 

 the ovarian wall are practically the same as in Cryptobranchus, 



