ACQUIRED CHARACTERS 43 



source of light. These are changes of external conditions 

 which modify the instinctive response. Internal or physio- 

 logical states of the animal may also modify the instinctive 

 responses. Thus, if the crustacean has been subjected to 

 mechanical stimulation (repeated touching with a sohd ob- 

 ject) its response may be altered. 



Again larvae of a barnacle for a few minutes after hatching 

 swim toward the light, then they turn and swim away from it, 

 a series of responses calculated to bring them to suitable 

 spots for attachment. The response has been modified 

 through some internal physiological change. Larvae of the 

 brown-tail moth, after their winter fast, are strongly positively 

 phototropic. They migrate up to the tips of the branches to 

 feed on the opening buds. If at this time they are brought 

 into the laboratory and placed in a test tube, they go toward 

 the window and will remain at the end of the tube toward the 

 window until they die, even if food is at the opposite end of 

 the tube a few inches away. After the larvae have fed they 

 are no longer phototropic. Digestion has probably destroyed 

 the substance in their bodies on which their phototropism 

 depended. (Loeb, Yale Review, July, 1915.) 



By such methods of studying the instincts of animals the 

 problem of instinct formation and inheritance may be simpli- 

 fied, through the elimination from it of all non-essential and 

 outside elements. 



As intelligence increases in the animal kingdom, we find 

 that instinct sinks more and more into a subordinate position. 

 In man there is very little inherited knowledge, if instinct 

 may so be regarded ; nearly everything has to be learned from 

 the beginning. Nevertheless it is an open question whether 

 intelligence has not increased through use, whether we do not 

 learn more easily for the reason that our ancestors have for a 

 million generations been learners. Of course I do not refer 

 here to formal education, but only to the exercise of such 

 intelligence as distinguishes man from other animals. May 

 not this have been evolved in part through use ? 



