32 IOWA ACADEMY OF SCIENCES. 



ORIGIN AND SIGNIFICANCE OF SEX. 



BY C. C. NUTTING. 



This paper is not presented as a contribution to our knowl- 

 edge of the subject of the origin of sex, so much as an attempt 

 to express coDcisely a theory of sex drawn from various sources,, 

 but principally from a work on the "Evolution of Sex" by 

 Geddes & Thomson, a work which seems to me to mark an 

 epoch in the science of philosophical biology. 



My excuse for presenting this subject before you to-night 

 lies in the fact that it has been my fortune within the past year 

 to personally investigate the origin of the sex-elements in one 

 group of animals, the hydroids, and to follow in the footsteps 

 of that great master August Weismann, whose studies have 

 given such an impetus to the search for truth in the realm of 

 sex and heredity. 



My own studies have resulted in a conviction that there is 

 truth in the theory advanced by Geddes & Thomson, and my 

 effort this evening will be to state this theory, in a slightly 

 modified form, in a series of definite propositions, each one of 

 which I believe to be defensible, ii not invulnerable. 



First, however, it will be necessary to call to your minds the 

 most important facts concerning reproduction among the one- 

 celled animals, or Protozoa. 



The simplest form of reproduction is that of the amoeba, in 

 which there is a simple division of the body mass of the parent 

 cell into two portions, each of which becomes an independent 

 organism. This is know^n as the process of reproduction by 

 fission. 



Turning to a somewhat higher group of Protozoa we find 

 another step introduced in the reproductive process. If we 

 study the Paramecium, for instance, we will find that it multi- 

 plies by fission, as does the amoeba, but that at intervals 



