238 Causes and Course of Organic Evolution 



indicate fundamental differences that are associated with 

 different mental functions. Furthermore, as one rises in the 

 animal scale from the simplest to the highest types, the in- 

 creasmg number of nerve cells, of groups of these as nerve 

 ganglia, of groups of such ganglia that constitute nerve or 

 brain centers, and finally the enlarging size of the brain in 

 the highest animals, all demonstrate a steady and advancing 

 complexity of the individual cells, that may be correlated 

 wdth like advance in the neuratin substance, as to its quantity 

 and correlation. So on the principle of environal action and 

 of proenvironal response, as animals have become exposed to 

 increasingly complex environal stimuli, these seem to have 

 started the formation of new and more intricate combinations 

 of the neuratin substance, that have very slowly resulted in 

 the formation of new and ever more complex as well as rapid 

 compounded resultant responses, which we designate habits, 

 instincts, intelligence, and intellect amongst others. 



But that such acquisitions are only slowly started might be 

 expected from the highly condensed and difficultly soluble 

 character of neuratin substance. This would be in entire accord 

 with the view held in the past decade by many, viz., that 

 heredity is greatly more uniform and persistent than is envir- 

 onal action, in the history of chains of organisms. Such, 

 however, should not blind us to the fast accumulating evidence 

 which demonstrates that mental associations and capacities 

 are gradually developed and persisted in by individuals. 



So in all afferent stimulatory acts that affect nerve cells, 

 and in all succeeding compounded resultants that start pro- 

 environal response amongst the higher invertebrates and 

 vertebrates, we accept it as proven that acquisition of new 

 lines of molecular motion which are satisfying to each organism 

 can occur. When moreover such is beneficial to the life and 

 successful reproduction of each individual, persistence of such 

 fines of motion develop into ''tendencies," and ultimately 

 into what have vaguely been called instincts. Thus the stud- 

 ies of V. Uexkull (87), of Allen (88: 293), of Spaulding (89: 49), 

 of Yerkes (90), of Edinger (91) and many others in recent 



