INSTINCT AND SENSUOUS COGNITION. 47 



pillars starve by trie aid of light in close proximity of 

 food. "The animals move to the window-side or to 

 the top of a test-tube in which they are kept. If, 

 then, a branch, covered with buds, is pushed into the 

 test-tube on the room side, the animals nevertheless 

 remain where light and gravity have compelled them 

 to go and are holding them. If, however, they once 

 are on the buds, the latter act as a stimulus which 

 may be even stronger than light. It is in such a case 

 impossible to draw the animals away from the food by 

 means of light. ' ' Besides these animals retain their 

 positive heliotropism only as long as they have not 

 yet eaten anything. ' 'As soon as they have eaten and 

 are about to moult, their irritability decreases and at 

 the time of moulting it is almost impossible to show 

 any effect of light or gravity upon them. ' ' 



We believe that Prof. Loeb's explanation contains 

 his refutation. For, if his theory were correct, all 

 caterpillars would be doomed in consequence of posit- 

 ive heliotropism. Caterpillars usually commence eat- 

 ing the buds of the highest twigs, and having devoured 

 all in their reach above them, they rest for some time, 

 until all is more or less digested. Now in order to 

 get new food, they must necessarily creep down to 

 another twig or tree. But this is impossible. For, 

 their "stomachs" being empty, the caterpillars are 

 positively heliotropic, and consequently they will all 

 die on the spot. This, however, is directly opposed 

 to the facts. There are no caterpillars in nature that 

 die in consequence of heliotropism or geotropism. 

 As long as they are hungry, they creep from one 

 branch to another and in all possible directions, until 



