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GENERAL EMBRYOLOGY 



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FIG. 92. Total views of the egg of the Tunicate Cynthia partita, showing the 

 changes in the arrangement of the materials of the egg subsequent to fertiliza- 

 tion. After Conklin. X 200. A. Unfertilized egg, before the fading out of the 

 germinal vesicle. Centrally is the mass of gray yolk; peripherally is the proto- 

 plasmic layer with yellow pigment, and surrounding the egg, the test cells and 

 chorion. B. About five minutes after fertilization, showing the streaming of the 

 superficial layer of protoplasm toward the lower pole, where the spermatozoon 

 enters, and the consequent exposure of the gray yolk of the upper hemisphere. 

 The test cells are also carried toward the lower pole. C. Side view of egg showing 

 the yellow protoplasm at the lower pole; at the upper pole a small clear region 

 where the polar bodies are forming. The location of the sperm pronucleus is also 

 indicated. D. Side view of egg shortly before the first cleavage, showing the 

 posterior collection of the pigmented protoplasm (yellow crescent) and the clearer 

 area above it. E. Posterior view of egg during the first cleavage, showing its 



