452 



WILSON. 



[Vol. XI. 



extremely conspicuous. During the pause they become much 

 shorter and less distinct, and in the living ^gg are nearly 



invisible, the aster be- 

 coming reduced ap- 

 parently to a clear 

 sphere lying at either 



V . / 



\ , \ . • : ,. 



/ 



— -^^-^^^W^^'S-C^^^-- ■■-■ --^-^ 



_..:_ •,.>-: 'A. .fi>^. •? M' ' ,.J-v,,-^^-_— 







''"wm 



B 



Fig. V. — Successive stages during the " pause." \c/. Photo- 

 types 5 and 6.] (25-30 minutes.) 



A . After complete fusion of the germ-nuclei to form the 

 cleavage-nucleus. Differentiation of the nuclear reticu- 

 lum has not begun, but the centrioles have increased in 

 number and form a group of granules in the center of 

 each aster. 



£. A stage slightly later than Fig. IV, the chromosomes 

 and spindle-fibres forming, the first indications of a 

 reticulum appearing in the central mass of each aster. 



C. Nuclear membrane disappearing, the reticular centro- 

 sphere established. 



pole of the nucleus. 

 Sections show, how- 

 ever, that the rays do 

 not disappear except- 

 ing at their outer ends, 

 which either break up 

 into the general retic- 

 ulum, or are with- 

 drawn towards the 

 basal portion. The 

 aster thus becomes 

 very small, consisting 

 of very thickly set 

 beaded rays extending 

 but a short distance 

 out from the central 

 mass, and staining in- 

 tensely blue. At this 

 period the rays have 

 lost their stiff and 

 fibrous appearance and 

 plainly consist of regu- 

 lar rows of rounded 

 blue granules arranged 

 in a single series at 

 their bases. The rays 

 are closely crowded, 

 so that the inner 

 portion of the aster 

 often gives the appear- 

 ance of a homogeneous 

 mass of blue granules, 



