MICRODISSECTION STUDIES. 



323 



mary. The germinal vesicle with an intact membrane is shown in 

 Fig. 6. Within thirty to forty-five minutes after standing in sea 

 water the nuclear membrane exhibits wrinkles and its outline be- 

 gins to fade from view. Within a few minutes no membrane is 

 visible and cytoplasmic granules can be seen moving into the region 

 hitherto occupied by the nucleus, while the nuclear sap appears to 

 be diffusing out (Fig. 6-c). As the nuclear membrane disappears 

 the nucleolus fades from view. The invasion of the nuclear area 

 by cytoplasmic granules continues until all of the area except a 

 small portion is rendered indistinguishable from the general cyto- 

 plasm of the egg. This small portion persists as the egg nucleus 

 (Fig 6e and /). In Fig. 6-g two consecutive positions of the 

 nucleus are shown. At 1:13 P.M. it lay deep in the substance of 

 the egg. In twenty minutes it had moved to the periphery of the 

 egg preparatory to the formation of the polar bodies. 



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FIG. 6. Camera lucida drawings of the successive steps in the normal 

 dissolution of the germinal vesicle in the maturing starfish egg. The proc- 

 ess was somewhat slowed down owing possibly to the compressed condition 

 of the egg necessary for detailed observation. 



FIG. 7. a, intact germinal vesicle within the egg. b, nucleus after having 

 been torn out of the egg and brought into sea water, c, d, e and /, successive 

 changes undergone by the nucleus lying in sea water. 



