MEMOEY IMAGES 169 



When this pigeon was almost a year old it was put into 

 a cage with a female pigeon, but although the female 

 aroused the sexual instinct of the formerly isolated male 

 the latter did not mate with her, but mated with the 

 hand of his attendant when the hand was put into the 

 cage, and this continued throughout the season. Thus the 

 memory images acquired by the bird at an impressionable 

 age and period perverted its sexual tropisms. 



It is perhaps of more importance to show that memory 

 images may have a direct orienting influence. The chemo- 

 tropic phenomenon of an insect laying its egg on a sub- 

 stance which serves as food (for both mother and off- 

 spring) and for which the mother is positively chemo- 

 tropic, may be modified by an act of associative memory, 

 e.g., when a solitary wasp drags the caterpillar on which 

 it lays its eggs to a previously prepared hole in the ground. 

 The essential part of the instinct, the laying of the eggs 

 on the caterpillar, does, perhaps, not differ very much 

 from the fly laying its eggs on decaying meat; and the 

 solitary wasp may be strongly positively chemotropic for 

 the caterpillar on which it lays the eggs, although this 

 has not yet been investigated. But the phenomenon is 

 complicated by a second tropism, which we will call the 

 orienting effect of the memory image. As is well known, 

 the w T asp before "going for" the caterpillar digs a hole 

 in the ground to which it afterwards drags the caterpil- 

 lar, often from a distance. The finding of this previously 

 prepared hole by the returning wasp, the writer would 

 designate as the tropistic or orienting effect of the memory 

 image of the location of this hole ; meaning thereby that 

 the memory image of the location of this hole makes the 

 animal return to this location. The conduct of these wasps 



