Sex as an Adaptation 449 
energy ; amphimixis must rather be advantageous for the 
maintenance and modification of species. As soon as we 
admit that amphimixis confers some such benefits, it is clear 
that the latter must be augmented, as the method appears 
more frequently in the course of generations ; hence we are 
led to inquire how nature can best have undertaken to give 
this amphimixis the widest possible range in the organic 
world.” Nature, Weismann says, could find no more effec- 
tual means of bringing about the union of the sexual cells 
than by rendering them incapable of developing alone. 
“The male germ-cells, being specially adapted for seeking 
and entering the ovum, are, as a rule, so ill provided with nu- 
triment that their unaided development into an individual 
would be impossible ; but with the ovum it is otherwise, and 
accordingly the ‘reduction division’ removes half the germ- 
plasm and the power of developing is withdrawn.” It can 
scarcely be claimed, in the light of more recent discoveries, 
that the reduction division takes place in order to prevent the 
development of the ovum, for how then could we explain the 
corresponding division of the male germ-cells? 
Whatever means has been employed to bring about the pro- 
cess of sexual reproduction, the guiding principle is supposed 
by Weismann to be natural selection as stated in the following 
paragraph: “If we regard amphimixis as an adaptation of 
the highest importance, the phenomenon can be explained in a 
simple way. I only assume that amphimixis is of advantage 
in the phyletic development of life, and furthermore that it is 
beneficial in maintaining the level of adaptation, which has 
been once attained, in every single organism; for this is as 
dependent upon the continuous activity of natural selection as 
the coming of new species. According to the frequency 
with which amphimixis recurs in the life of a species, is the 
efficiency with which the species is maintained; since so 
much the more easily will it adapt itself to new conditions of 
life, and thus become modified.” 
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