DIFFERENT KINDS OF INSTINCT 113 



knows not that an animal is to proceed from the egg, and fir 

 less that this animal must be nourished with other animals, 

 she collects ten or twelve small green worms, which she piles 

 one above another, rolls them up in a circular form, and fixes 

 them in the hole in such a manner that they cannot move. 

 When the wasp-worm is hatched, it is amply stored with the 

 food nature has destined for its support. The green worms 

 are devoured in succession : and the number deposited is ex- 

 actly proportioned to the time necessary for the growth and 

 transformation of the wasp- worm into a fly, when it issues 

 from the hole, and is capable of procuring its own nourish- 

 ment. 



There are many other instances of ichneumon-wasps and 

 flies, which, though they feed not themselves upon worms, lay 

 up provisions of these animals for the nourishment of their 

 young ; and each kind is adapted to trfe constitution of the 

 worm that is to proceed from their eggs. 



Birds of the same species, unless when restrained by pecu- 

 liar circumstances, uniformly build their nests of the same 

 materials, and in the same form and situation, though they 

 inhabit very different climates. When removed by necessity 

 from their eggs, they hasten back to them with anxiety. They 

 turn and shift their eggs, which has the effect of heating them 

 equally. Ducks and geese cover up their eggs till they re- 

 turn to the nest. A hen sits with equal ardor upon eggs of a 

 different species, or even upon artificial eggs 



The spider, the dermestes, and many insects of the beetle 

 kind, exhibit an instinct of a very uncommon nature. When 

 put in terror by a touch of the finger, the spider runs off with 

 great swiftness ; but if he finds that, whatever direction he 

 takes, he is opposed by another finger, he then seems to de- 

 spair of being able to escape, contracts his limbs and body, 

 lies perfectly motionless, and counterfeits every symptom of 

 death. In this situation, I have pierced spiders with pins, 

 and torn them to pieces, without their discovering the smallest 

 mark of pahi. This simulation of death has been ascribed 

 to a strong convulsion, or stupor, occasioned by terror. But 

 this solution of the phenomenon is erroneous. I have re- 

 peatedly tried the experiment, and uniformly found, that, if 

 the object of terror be removed, in a few seconds the animal 

 runs off with great rapidity. Some beetles, when counter- 

 feiting death, suffer themselves to be gradually roasted with- 

 out moving a single joint. 

 10* 



