1897.] 



NEW YORK ACADEMY OF SCIENCES. 



391 



a delicate spindle of few fibers, and about each centrosome is a 

 distinct radiation, resulting from the division of the single aster. 

 In some cases the radiation about the centrosome more distant 

 from the sperm-head is seen to be smaller than the other, but it 

 is not certain that this is always the case. Fig. 5 shows a 

 sperm-head accompanied by two centrosomes with spindle and 

 astral radiations. In another section of this egg the second 

 polar body is seen to be in process of formation. 



After the formation of the second polar body the spindle- 

 fibers disappear and the centrosomes enlarge, forming small ves- 

 icles, which unite to give rise to the female pronucleus. At this 

 stage the " female " centrosome or centrosomes disappear. The 

 central region of the aster appears to consist of a fine network, 

 and the rays become less distinct, seeming to fade away in the 

 cytoplasm. This is shown in Fig. 6,/, in which the female pro- 

 nucleus is formed and enlarging, having "already become less 

 dense. It has left its original position and is moving toward 

 the central portion of the egg. 



Fig. 5 



Fig. 6 



In Fig. 6* at m is seen the male pronucleus with the accom- 

 panying cytoplasmic structures as the}' now appear. The two 

 centrosomes have disappeared, the polar regions of the spindle 

 being occupied by a fine network. The rays are evidently dis- 

 integrating and the spindle is barely indicated in the cytoplasm. 

 These structures present this appearance Avith regularity at this 

 stage. It is certainly not due to imperfect fixation or to other 

 errors in technique, for on the same slides are eggs in somewhat 

 earlier stages with distinct " male " centrosomes, spindle and 

 radiations. The following stages afford a further confirmation 



*Fig. 6 is a combination of two sections of the same egg, one of which contained the 

 emale, the other the male elements. 



