GERMINAL VESICLE 

 (NUCLEAR MATERIAL) 



YELLOW 



PIGMENTE D 



CYTOPLASM 



(PERIPHERAL 



, PROTOPLASM 



TEST CELLS 



SP E R M, 

 CLEAR PROTOPLASM 



YOLK MATERIAL 



VAGE PLANE 

 OLAR BODIES 



Fig. 132. Movement of ooplasmic substances in the egg of Styela (Cynthia) partita 

 at the time of fertilization. (All figures after Conklin, '05.) (A) Unfertilized egg after 

 the disappearance of the nuclear membrane of the germinal vesicle. The gray yolk is 

 shown in the center of the egg. surrounded by the yellow-pigmented cytoplasm. The test 

 cells and chorion surround the egg. (B) Egg five minutes after fertilization, showing 

 the streaming of the peripheral protoplasm indicated by arrows toward the vegetal pole, 

 where the sperm has entered. The gray yolk is shown in the upper part of the egg below 

 the nuclear material. The clear protoplasm, derived from the nuclear sap of the germinal 

 vesicle, also flows down with the peripheral protoplasm. (C) Side view of an egg after 

 peripheral protoplasm has migrated to the vegetal pole of the egg. The clear protoplasm 

 is shown at the upper edge of the yellow cap. The polar bodies are forming in the 

 midpolar area (MP.) at the animal pole. (D) Side view of the egg showing the yellow 

 crescent and the area of clear protoplasm above the yellow crescent. The yolk material 

 is shown at the vegetal pole below and to one side of the yellow crescent. (E) Yellow 

 crescent and clear protoplasm viewed from the posterior pole of the egg. Animal pole 

 is above the crescent; yolk material is below. (F) Same view as (E) a little later, 

 showing the external beginnings of the first cleavage. The polar bodies are shown above 

 the crescent material. (G) View similar to that of (E, F) a little later. The first cleavage 

 is complete. Observe that the clear protoplasm and the yellow crescent have been bisected 

 equally. The cleavage plane corresponds to the median axis of the embryo. 



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