234 METAMORPHOSIS AND 



disuse, since those larvae which are destitute of legs 

 do not go in search of food but either live in the 

 midst of it or are fed by others, and that the pro-legs 

 of the caterpillar have been developed by the 

 muscular action of the insect in clinging to leaves. 

 Here again the hormone theory, although we cannot 

 pretend to understand the matter completely, helps 

 us to form a conception of the process of heredity and 

 evolution. The disuse of legs in the larva affects the 

 determinants, so that they remain inactive in the 

 presence of the hormones produced in the body 

 generally in this stage. In the adult stage activity 

 of the legs produces hormones which influence the 

 same determinants in the gametes, to develop legs, 

 but again in the presence of the different hormones 

 which are present in the body generally in the adult 

 stage. As the habits of larva and adult became 

 more specialised and contrasted, the change became 

 less and less gradual, and the intermediate stage, not 

 being adapted to any transitional mode of life, 

 became an inactive pupa in which the adult organs 

 develop. 



In conclusion I will briefly consider the attempts 

 which have been made to prove the influence of 

 somatic modifications or characters on the gametes 

 by direct experiment. The method of Kammerer of 

 inducing changes of habit or structure by conditions, 

 and then showing that the change is in some degree 

 inherited, has already been mentioned. One 

 obvious criticism of this evidence is that it seems to 

 prove too much, for it is difficult to believe that a 

 change produced in individuals would show so much 

 hereditary effect in their immediate offspring. 

 Two other methods are conceivable by which the 



