POLYMORPHISM IN SPECIES. 197 



growth. Thus we see, in the workers which have 

 been deprived of their full growth by lack of nour- 

 ishment, the strongly developed female instinct of 

 caring for the young and building the house. This 

 instinct is probably perfected in each individual 

 largely by its constant exercise. It is probable also 

 that the growth of individuals in a social body, espe- 

 cially the psychic growth, would be affected in some 

 way by the mysterious sympathetic nervous influ- 

 ence which shows itself among animals in the stam- 

 peding of cattle, the orderly wheeling and circling 

 of flocks of birds, in the movements of droves of 

 caterpillars and swarms of insects, and by the phe- 

 nomena of suggestion and hypnotism in man. These 

 instincts might be cultivated by some psychic influ- 

 ence, and, in turn, the instincts may influence the 

 bodily growth. The final conclusion of modern sci- 

 ence is, that no cause is too slight to produce an 

 effect. 



