EVOLUTIONARY THEORIES SINCE DARWIN 239 



velopment. This throwing away is quite as effective 

 for all its descendants. Any ancestral quality now 

 lost is lost from the line forever. In the formation 

 of the sperm cell set free by the male a similar throw- 

 ing away of one-half the characters has taken place. 

 The Qgg cell and the sperm cell fuse together. There 

 are as many possibilities now as there were in either 

 parent, but not all the potentialities of both parents. 

 Half the possibilities of each have been thrown away, 

 and hence cannot appear in the offspring. By this 

 constant process we get, in every generation, new 

 combinations of qualities. This is the main cause, 

 says Weissman, for variations. 



There is, however, another possible cause. Each 

 cell has enough determinants in it for many indi- 

 viduals, and it seems to be more or less a matter of 

 accident which qualities shall come out. It has been 

 suggested that as an tgg lies within the gland, a 

 blood vessel may bring blood to it in such way that 

 a determinant, lying in a certain position in the egg, 

 may get the richest supply of blood, and hence de- 

 velop at the expense of the less nourished determi- 

 nant. By these two methods variation comes into 

 an animal's life, if Weissman and his school are to 

 be believed. 



This is a serious blow, if true, to many theories of 

 evolution. The great mass of evolutionists still feel 



