FERTILIZATION 



119 



cilia maintains its identity much longer and may be 

 distinguished throughout the early development of the 

 embryo, but it finally 

 merges with the proto- 

 plasm of the egg. 



As the sperm nucleus 

 moves toward the egg 

 nucleus, it enlarges some- 

 what, and the two nuclei 

 soon come into contact 

 (Fig. 61). At the time 

 of contact both nuclei are 

 in the resting condition, 

 and this condition con- 

 tinues even after the 

 nucleus of the sperm has 

 become more or less 

 imbedded in that of the 

 egg. From this point the 

 development must be 

 exceedingly rapid, for the 

 next stage observed 

 showed the division of 

 the nucleus formed by the 

 fusion of the two nuclei 

 of the egg and sperm, the 

 first division in the 

 sporophyte generation. 

 This stage is illustrated 

 by Fig. 62 in the next 

 chapter. The fact that this division, at the stage repre- 

 sented in the figure, shows only half the number of 



W: 



Fig. 61 . — S I a n geria paradoxa, 

 showing fertilization; the sperm 

 nucleus is entering the nucleus of 

 the egg; the spiral, ciliated band of 

 the sperm remains at the top of the 

 egg. Highly magnified. 



