ORIGIN OF LIFE, SEX, SPECIES, ETC. 221 



As specialization advances, the occasion for 

 locating reproductive cells and organs near the 

 center of the organism is, however, subordinated to 

 other requirements; for the organs of specialized 

 types of life must obviously be naturally selected, 

 mainly with reference to their fitness to furnish 

 the organism protection against deleterious influences 

 arising in the environment, and provide it with 

 opportunities for sustaining and propagating life. 

 Furthermore, in specialized organisms life depends 

 on harmonious co-operation of all the organs. The 

 form of organs and of the whole organism must, 

 therefore, be naturally selected with reference to 

 these two requirements : fitness for protection, and 

 opportunities for harmonious co-operation ; and these 

 limitations are incompatible with centrality for the 

 reproductive cells and organs. 



Origin of Sex 



The simplest kind of reproduction is hard to dis- 

 tinguish from mere overgrowth. When a unicellu- 

 lar organism has, by assimilation, grown so large 

 that the motions of the extremities can no longer be 

 controlled by the forces at the center, then these 

 remote portions organize a cell of their own by cary- 

 okinesis, fission, etc. The internal circulation and 

 the brief time between birth and reproduction in 

 these simplest forms of life effectually prevent the 

 differentiation between central and external sub- 

 stance reaching a degree, which would justify the 



