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 egg 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 egg 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 
