THE LIVING MACHINE BUILDING FACTORS. 163 



of the cell is such that it requires in the ordinary 

 process of reproduction the union of germinal 

 material from two different individuals to pro- 

 duce a cell which can develop into a new indi- 

 vidual. As we have seen, the egg gets rid of half 

 its chromosomes in order to receive an equal 

 number from a male parent ; and thus the fer- 

 tilized egg contains chromosomes, and hence 

 hereditary material, from two different individ- 

 uals. Now, this sexual reproduction occurs very 

 widely in the organic world. Among some of 

 the lowest forms of unicellular organisms it is 

 not known, but in most others some form of such 

 union is universal. Now, here is plainly an abun- 

 dant opportunity for congenital variations; for 

 it is seen that each individual does not come from 

 germ material identical ^vith that from which either 

 parent came, but from some of this material mixed 

 with a similar amount from a different parent. Now, 

 the two parents are never exactly alike, and hence 

 the germ plasm which each contributes to the off- 

 spring will not be exactly alike. The offspring 

 will thps be the result of the unfolding of a bit 

 of germ plasm which will be different from that 

 from which either of its parents developed, and 

 these differences will result in congenital variations. 

 Sexual reproduction thus results in congenital 

 variations; and if congenital variations are neces- 

 sary for the evolution of the living machine and 

 we shall soon see reason for believing that they 

 are we find that sexual reproduction is a device 

 adopted for bringing out such congenital varia- 

 tions. 



Inheritance of Variations. The reason why 

 congenital variations are needed for the evolution 

 of the living machine is clear enough. Evanescent 



