OBSERVATIONS AND EXPERIMENTS 215 



into sea water. The animal became acclimatised and 

 presented certain modifications (loss of hair, etc.) 

 which became more deeply marked in the following 

 generations. The most important fact, however, was 

 that after several generations the Tubifecc had become 

 absolutely unable to live in its original environment. 

 In this case the influence of the environment seemed 

 to continue after the environment had changed. 



More systematic and convincing experiments have 

 been made with a view to determining the variations 

 produced in the caterpillars of some butterflies by 

 different kinds of environment. Butterflies are es- 

 pecially %asy to study; therefore many scientists have 

 placed caterpillars under different conditions of tem- 

 perature, light, food, etc., and observed the influence 

 of those various factors on the adult and its progeny. 



Kellogg and Bell fed the larva? of Bornbyx mori, 

 or silkworm, varying quantities of mulberry leaves or 

 replaced mulberry leaves by lettuce leaves. 5 A scanty 

 allowance of food produced a decrease in the size of 

 the imago and that decrease was apparent even in the 

 third generation, although the larvae of the first and 

 second generations had received a normal quantity of 

 food. After two or three successive generations were 

 kept on a low diet there arose a dwarf breed of silk 



5 Variations induced in larval, pupal and imaginal stages of Bombyx 

 mori by controlled varying food supply. (Science, XVIII, 1903, pp. 741- 

 748.) 



