90 MIND IN EVOLUTION CHAP. 



to experience. There are adaptations which cannot be 

 explained by any interaction of purely hereditary tendencies, 

 and there are cases in which the whole structure of the 

 instinct is profoundly modified by the experience of the 

 individual. 



The habits of solitary wasps have lately been the sub- 

 ject of a charming monograph by two very careful 

 observers, who have corrected the somewhat startling con- 

 clusions of earlier naturalists, and have made a notable 

 contribution to the whole question of Instinct. 1 I may 

 quote some of their observations : 



" When the provisioning is completed the time arrives for the 

 final closing of the nest, and in this, as in all the processes of 

 Ammophila, the character of the work differs with the individual. 

 For example, of two wasps that we saw close their nests on the 

 same day, one wedged two or three pellets into the top of the 

 hole, kicked in a little dust and then smoothed the surface over, 

 finishing it all within five minutes. This one seemed possessed 

 by a spirit of hurry and bustle, and did not believe in spending 

 time on non-essentials. The other, on the contrary, was an 

 artist, an idealist. She worked for an hour, first filling the neck 

 of the burrow with fine earth which was jammed down with 

 much energy, this part of the work being accompanied by a loud 

 and cheerful humming, and next arranging the surface of the 

 ground with scrupulous care, and sweeping every particle of dust 

 to a distance. Even then she was not satisfied, but went 

 scampering around hunting for some fitting object to crown the 

 whole. First she tried to drag a withered leaf to the spot, but 

 the long stem stuck in the ground and embarrassed her. Relin- 

 quishing this, she ran along a branch of the plant under which 

 she was working, and leaning over, picked up from the ground 

 below a good sized stone, but the effort was too much for her, 

 and she turned a somersault on to the ground. She then started 

 to bring a large lump of earth, but this evidently did not come up 

 to her ideal, for she dropped it after a moment, and seizing an- 

 other dry leaf carried it successfully to the spot and placed it 

 directly over the nest." 2 



We find here, first, variation as between individuals, so 

 marked that we can hardly suppose heredity alone to 

 account for the details of each method. Secondly, what 



1 Instincts and Habits of Solitary Wasps, by Mr. and Mrs. Peckham ; 

 Wisconsin Geological and Natural History Survey, Bulletin No. 2. 



2 P. 21. 



