EMBRYOLOGY OF CRYPTOBRANCHUS 



123 



represent the anlage of the germinal disc or blastodisc, which later 

 comes to enclose the germinal vesicle and the cytoplasm accumu- 

 lated beneath it. Elsewhere a very thin peripheral layer of fine 

 yolk particles, continuous with the yolk disc, lies immediately 

 beneath the protoplasmic mantle. The interior of the egg shows 

 no particular change in the yolk. 



The germinal vesicle is spherical when perfectly preserved; 

 when flattened this is due to shrinkage. The ground-substance 

 or nuclear sap appears homogeneous under a low power, but with 



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Fig. 25 Central portion of the germinal vesicle represented in the preceding 

 figure, enlarged to show details. The finely granular ground-substance of the ger- 

 minal vesicle is not shown. X 340. c. g., chromatin granules; chr., chromo- 

 somes; nu., nucleolus. 



a magnification of 500 diameters it exhibits an extremely fine but 

 dense granular structure. The nucleoli are now nearly all aggre- 

 gated at the center; some few persist at the periphery, particularly 

 on the side toward the center of the egg. The chromosomes are 

 for the most part confined to the central part of the area occupied 

 by the nucleoli. 



Among the nucleoli, though not closely associated with them, 

 there are now found very numerous and minute granules which 



