248 DEVELOPMENT AND HEREDITY. 



of the lower animals which reproduce parthenoge- 

 netically, when food is plenty and other conditions 

 favourable, only females are produced, but when the 

 conditions of life reach a certain degree of severity, 

 males are produced. In Professor Yung's experi- 

 ments with tadpoles, we saw that reducing the 

 variety of stimuli by limiting the food to only one 

 kind, had the effect of greatly increasing the per- 

 centage of females above the normal ratio. 



To the inquiry, what are the most advantageous 

 conditions for life and development, not only for the 

 lower animals, but for man also, it may be answered 

 — great variety and strength of stimuli. As the 

 stimuli cannot all be of the same kind or cannot all 

 be pleasant and agreeable without decreasing the 

 variety, so adversity has its uses ; and the strength 

 of the stimuli of adversity counts equally with the 

 stimuli of prosperity ; and perhaps more, for adversity 

 has more varieties than prosperity. What counts 

 chiefly is not the available supply of simple energy, 

 but the complexity of the forces acting. The parasite 

 buried in the body of its host, has a comparatively 

 boundless supply of energy at its command, but 

 nevertheless degenerates, for it is removed from the 

 operation of the forces which cause development. 

 Great wealth, unless accompanied by corresponding 

 anxieties, duties, and responsibilities, removes its 



