No. 2.] 



THE SEA-URCHIN EGG. 



449 



detailed history of the chromatin will be considered under 

 another head, but a brief statement regarding the nuclei will be 

 useful here. After coming into contact with the egg-nucleus 



r^^^■^::Vi>^ 



Fig. II. — Approach of the germ-nuclei showing the growth of the sperm-nucleus and aster and 

 the branching of the rays. \cf. Phototype 3.] (6-8 minutes.) 



the sperm-nucleus rapidly enlarges, its substance becomes 

 reticular, and it assumes a vesicular form. It then flattens 

 down closely against the egg-nucleus and assumes a lens-shape ; 

 the boundary between it and the egg-nucleus then fades away, 



