Nature of Sexual Diversity 119 



an actual attraction of some sort between the two kinds of 

 substance when separated, and this it is which causes them 

 to unite. In the case of entire individuals, and particularly 

 in higher organisms, this attraction must of course work 

 through many indirect means, but in the actual union of 

 male and female nuclei or of chromosomes (Figure 29) it 

 must show itself in some direct and simple manner, as when 

 two chemicals unite (compare Doflein, 1911, page 260). 

 The cause of the union is the diversity. Thus, according to 

 this view, the attraction of the sexes has its basis in the 

 foundations of life. 



To be consistent, this theory has to maintain that in 

 the union of the chromosomes in pairs, which appears to 

 be the elementary act in mating, there is this same diversity 

 between the two uniting members, and that this is the cause 

 of their union. 



Further, it would appear that according to this view, 

 growing old is fundamentally a different thing in the two 

 sexes ; in the female it would be the consequence of an excess 

 in the vegetative functions ; in the male a consequence of ex- 

 cess in the kinetic -functions. This consequence I have not 

 seen drawn, but it appears an unavoidable one if the theory 

 is held. Doubtless in each sex it could be held that some other 

 processes essential to life are interfered with through these 

 changes, in such a way as to give similar outward signs of 

 age, such as we s.ee in the two sexes of higher organisms. 



Let us now turn back to the conjugation of Paramecium 

 and see its relation to such ideas. 



First, of the two individuals that mate, each plays the 

 part of both male and female. Each furnishes a smaller, 

 active half nucleus, which moves over to join the larger in- 

 active half nucleus of the other individual; this active half 

 nucleus evidently takes the role of the male germ cell. But 



