466 WESLEY E. COE, 



not seen later. The radiations about the egg-nucleus remain visible 

 until the germ- nuclei are nearly ready to fuse. 



The spermatozoon may enter the egg at any point, but in the 

 great majority of cases its place of entrance is in the pole of the 

 egg which lies opposite the polar bodies, or the point where they are 

 to be formed. 



The aster-fibres are not attached to the centrosomes directly, but 

 are rather directly continuous with the substance of the centrospheres, 

 into which they often penetrate for a considerable distance, but never 

 quite so far as to the centrosome. 



The centrosome of the sperm-aster early divides into two; the 

 daughter - centrosomes move apart with the formation of a beautiful 

 central spindle. The fibres of the original aster become arranged at 

 right angles to this central spindle; those at its ends are collected 

 into two groups about the daughter centrosomes, while those nearer 

 its equator degenerate. 



The central spindle is torn asunder by the further separation of 

 the centrosomes, and its fibres are apparently transformed into aster- 

 fibres. 



The two asters thus formed may separate widely or remain near 

 together. They may slightly precede the sperm-nucleus towards the 

 centre of the egg, or may leave it far behind. In all cases, however, 

 they come to lie near together between or beside the germ-nuclei when 

 these are nearly ready for fusion. 



The sperm-asters reach their greatest development just before the 

 union of the germ-nuclei. At this time their fibres extend in all 

 directions nearly to the periphery of the cell, and often form a marked 

 decussation above the egg-nucleus. They then begin to degenerate, 

 however. Their centrosomes lose their centrospheres, lie free in the 

 cytoplasm, and in the vast majority of cases eventually disappear. 

 The aster-fibres break up into rows of granules throughout their whole 

 length almost simultaneously, yet these rows often retain their identity 

 (and therefore mark the former positions of the aster-fibres) until the 

 cleavage-asters are well formed. 



In a few preparations it may be determined with a good deal of 

 certainty that the cleavage - centrosomes are identical with those of 

 the sperm-asters, for the new asters (which are to form the cleavage- 

 asters) occasionally begin to develop to a slight extent even before 

 the complete fusion of the germ-nuclei, and before the degeneration 

 of the old aster-fibres has gone on to any considerable extent, in 



