114 THE ORIGIN AND EVOLUTION OF LIFE 



reaction and trial. Thus the behavior of organisms is of such 

 a character as to provide for its own development. Through 

 the principle of the production of varied movements and that 

 of the resolution of one physiological state into another, any- 

 thing that is possible is tried and anything that turns out to 

 be advantageous is held and made permanent.^ Thus the sub- 

 psychic stages when they evolve into the higher stages give us 

 the rudiments of discrimination, of choice, of attention, of 

 desire for food, of sensitiveness to pain, and also give us the 

 foundation of the psychic properties of habit, of memory, and 

 of consciousness.'- These profound and extremely ancient 

 powers of animal life exert indirectly a creative influence on 

 animal form, whether we adopt the Lamarckian or Darwinian 

 explanation of the origin of animal form, or find elements of 

 truth in both explanations.^ The reason is that choice, dis- 

 crimination, attention, desire for food, and other psychic 

 powers are constantly acting on individual development and 

 directing its course. Such action in turn controls the habits 

 and migrations of animals, which finally influence the laws of 

 adaptive radiation^ and of selection. In this indirect way these 

 psychic powers are creative of new form and new function. 



In the evolution of the Protozoa^ the starting-point is a 

 simple cell consisting of a small mass of protoplasm contain- 

 ing a nucleus within which lies the heredity-chromatin 

 (Fig. 12). This passes into the plasmodial condition of 

 the Rhizopods, in which the protoplasm increases enormously 

 to form the relatively large, unprotected masses adapted to 



'Jennings, H. S., 1906, pp. 318, 319. . "Op. cit., pp. 329-335- 



^ These two explanations are fully set forth below (see pp. 143-146) in the introduc- 

 tion to the evolution of the vertebrates. 



■* Adaptive radiation — the development of widely divergent forms in animals ances- 

 trally of the same stock or of related stocks, as a result of bodily adaptation to widely 

 different environments (see p. 157). 



^ Minchin, E. A., 1916, p. 277. 



