INTRODUCTION 15 



and continue by division, and one body' separates 

 from the other. The cells remain the same. This 

 is one form of asexual reproduction. The germ- 

 plasm, which lies wrapped up in the nucleus of each 

 cell, is in this case removed into a different room, as 

 it were, whereas in sexual reproduction the entire 

 rearrangement of the special germ-cell which carries 

 on the race may be compared, on fusion with the 

 sperm of the opposite sex in a different flower, with 

 the building of a new house from an old with the 

 same materials^ but arranged on a different plan. A 

 sperm-cell and an egg-cell fuse, division occurs, both 

 nuclear and cell-division. In the ripe egg-cell the 

 sperm-nucleus fuses with the egg-nucleus, and the 

 chromosomes of the former are added to those of the 

 latter and are thus doubled, remaining distinct but 

 joined at the extremity, but half are removed so that 

 the original number remains. The paternal and 

 maternal characters in both sperm- and egg-cell were 

 first halved in the cell-division and nuclear-division 

 preceding fertilisation. After reduction and division 

 or mitosis, the paternal chromosomes and characters 

 of each are brought together with the maternal cha- 

 racters of each, and in place of one kind there are 

 two kinds. In the case of the male and female cells 

 the grandmother cells^ formed from the sporogenous 



* The segregation of chromosomes by the division of the grand- 

 mother cells is the reverse of the process when the egg is fertilised, 

 where the number of chromosomes is doubled, whilst in the former 

 it is halved. We may thus speak of an x generation and a 2x gene- 

 ration. This is conformable with Mendel's laws. 



