Nature of Sex 109 



regard to this strange process. First, is this union a neces- 

 sity of life? That is, could and would life continue with- 

 out its occurrence? Could and would development occur 

 without it? Is there some single general result produced 

 by mating, something as general as the production of 

 energy through the taking of food? If there is, what is this 

 single general effect of mating? This is the real point 

 underlying the much-discussed question: What is the pur- 

 pose of mating? 



Certain other questions arise from the differences between 

 the two sexes. What is the nature of this difference? That 

 is, is there a single kind of chemical or physiological dif- 

 ference between the sexes, wherever sex differences occur; a 

 fundamental diversity of which all other sex diversities are 

 consequences? And does this diversity exist whenever there 

 is union of individuals or cells or parts of cells? 'Are the 

 two chromosomes that unite diverse in this manner? And 

 are all the unions that occur a consequence of such diver- 

 sity? Or may two precisely similar individuals or cells or 

 chromosomes unite at mating? Again, is this sex differ- 

 ence coextensive with life, so that all living things are com- 

 posed of two classes of substance, male and female, as 

 some have asserted? Or is sex difference something that 

 pertains only to certain kinds of organisms ; perhaps some- 

 thing that has arisen during evolution, like the difference 

 between two species of plants or animals? 



We shall examine the facts in the Protozoa in their bear- 

 ing on these questions, and shall try to determine with which 

 answers these facts agree best. We will take up the process 

 of union first in what is perhaps the best known and most 

 instructive case in these lower organisms, in the infusorian 

 Paramecium. Then we shall compare what happens in this 

 animal with what occurs in others, keeping in mind through- 

 out the fundamental questions that we have set forth. 



