12 



6. Reaction of the Individual to its Environment. 



Use and disuse. 

 Heliotropism and geotropism. 



Chemotropism. 

 Thigmotropism. 

 Temperature and color. 



Summer and winter coats. 



Seasonal dimorphism. 



Experiments of Weismann (Studies in the The- 

 ory of Descent, Vol. i, p. i and p. 126), and 

 of Edwards (Butterflies of North America, 

 Vol. I, pp. 7-16). 



Summer form changed to winter form by cold. 



Winter form not changed by heat. 



Poulton's experiments. 



The determination of sex. 



(See Geddes and Thomson, Evolution of Sex, pp. 32-54.) 



Mrs. Treat's experiments on caterpillars. 



Young's " " tadpoles. 



GiROu's " " sheep. 



The Aphides. 



The honey-bee. 



Maupas's experiments on Hydatina. 



(See Watase, Journ. Morph. Vol. 6, p. 483.) 

 Summary. 

 Individual acclimatization. 

 Reactions following change of medium. 



Experiment on frog tadpoles. 

 Amblystoma tigrinum. 

 Experiments of Schmankewitsch. 



Artemia salina. 



Artemia milhausenii. 



Branchinecta schaefferi. 



