392 



TRANSACTIONS OF THE 



[DEC. 13, 



of the view that this disintegration is a part of the normal his- 

 tory- of these structures, for a little later there is no trace of 

 asters or spindles in the egg. 



The pronuclei increase still further in size and show the 

 chromatin in the form of a long thread. Meanwhile they ap- 

 proach each other. At a stage when they are near together, 

 but before contact occurs, they are seen to be surrounded by 

 an area in which the cytoplasm possesses a reticular structure. 

 Outside of this and about it as a center a distinctly radiate ar- 

 rangement of the cytoplasm is found. This is evidently not an 

 aster, although its rays are probably perfectly similar in nature 

 to astral rays. There is no trace of centrosome or true aster in 

 the egg. The radiate arrangement of the cytoplasm appearing 

 at this time is evidently the expression of some activity within 

 the egg. It ma^' perhaps be due to the absorption of liquid 

 from the cytoplasm by the pronuclei in their rapid growth, and 

 decrease in density-. This may result in c^'toplasmic contrac- 

 tion, the network being stretched in a radial direction. The re- 

 ticular appearance of the region about the pronuclei ma}' indi- 

 cate that there is an accumulation of liquid there. 



F'g 8 



Now, at the stage shown in Fig. 7, just before the i)ronuclei 

 come into contact, two extremely minute asters appear in the 

 plane of copulation, one on either side of the pronuclei. These 

 are clearly seen to have no relation to the large radiation just 

 mentioned. At first it is impossible to distinguish any definite 

 centrosome at their centers, but they grow rapidly and a centro- 

 some soon becomes visible in each, though at first extremely 

 small. The two pronuclei now lie in contact. They are still 

 larger than before, and the chromatin threads are clearly visible. 



The two asters become large and distinct, and some of the 

 rays are seen to end in the nuclear membranee of both pronuclei. 

 This stage is shown in Fig. 8. The pronuclei are elongated in 



