i 5 6 THE EVOLUTION OF SEX. 



does the alleged inheritance of acquired characters, he finds the 

 fountain of change in sexual reproduction. "Sexual reproduction 

 is well known to consist in the fusion of two contrasted reproductive 

 cells, or perhaps even in the fusion of their nuclei alone. These 

 reproductive cells contain the germinal material of keimplasma, and 

 this again, in its specific molecular structure, is the bearer of the 

 hereditary tendencies of the organisms from which the reproductive 

 cells originate. Thus in sexual reproduction, two hereditary tend- 

 encies are in a sense intermingled. In this mingling, I see the cause 

 of the hereditary individual characteristics; and in the production of 

 these characters the task of sexual reproduction. It has to supply 

 the material for the individual differences from which selection 

 produces new species." 



But this very reasonable contention hardly appears to consist 

 with Weismann's quantitative interpretation of the process of fertili- 

 zation. Nor is it evident how the diversities of the male and female 

 plasmas became such as their results indicate them to be, if Weismann 

 be correct in maintaining that no modifications of the body influence 

 the reproductive elements. 



Brooks and Weismann have at anv rate maintained a thesis which 

 we will be inclined to oppose, that sexual union is productive of 

 variation. To discuss the relations of this view to other theories of 

 variation is not here revelant, nor can we do more than mention the 

 reasonable suggestion of Hatschek, that sexual reproduction is a 

 remedy against the operation of injurious variations. For we can 

 readily imagine that the excess of some particular line of anabolic or 

 katabolic differentiation may be neutralized through fertilization. In 

 this way one is led to speculate as to whether the constant pairing 

 of diseased individuals may not sometimes be more mercifully con- 

 doned by nature than we have been accustomed to think. 



