POLYMORPHISM. 109 



but in spite of all I cannot feel perfectly sure that I have influenced in 

 any unusual way the growth of a single individual." 



This rather unsatisfactory answer, to the question as to whether 

 quantity or quality of food or both, have an ergatogenic value, has 

 led some investigators to seek a solution along more direct lines. 

 Thus O. Hertwig and Herbst suggest that the morphogenic stimulus 

 may be furnished by some internal secretion of the reproductive 

 organs. This, too, is possible, but owing to our very imperfect knowl- 

 edge of the internal secretions, even in the higher animals, we are not 

 in a position either to accept or reject this suggestion. 



\Ye may conclude, therefore, that while the conception of the 

 worker phase as the result of imperfect nutrition is supported by a 

 considerable volume of evidence, we are still unable to understand 

 ln>\v this result can take on so highly adaptive a character. Such a 

 concise effect can hardly be due to manifold and fluctuating external 

 causes like nutrition, but must proceed from some more deeply seated 

 cause within the organism itself. Of course, the difficulty here en- 

 countered is by no means peculiar to polymorphism ; it confronts us at 

 every turn as the all-pervading enigma of living matter. 



