1 66 Instinct, 



by the joint products of the body and instinct of 

 the cocoon-builder. The parasites fed upon the 

 chrysalis of the insect, and they were protected, dur- 

 ing their transformation, by the cocoon which he 

 had prepared for his own transformation. 



The common Bot-fly is another example of the 

 dependence of one animal upon another, for the 

 completion of the work, which its Instinct has be- 

 gun. This fly deposits her ^g% upon the hair of the 

 horse, where it is held by a glue that instantly hard- 

 ens. If the work were left where the mother leaves 

 it, there would soon be an end of the species. But 

 she deposits her eggs, instinctively, on such parts 

 of the body of the horse that he will swallow more 

 or less of them. When the eggs or larvce have 

 reached the horse's stomach, they have found the 

 proper place for development, — a place which the in- 

 sect mother cannot reach, and having no connec- 

 tion with the parts where the eggs are deposited. 

 But the fly, as though understanding the whole 

 process and the calculation of chances, puts her 

 eggs in such a position, that enough of them shall 

 reach their place of development, to keep the spe- 

 cies good. 



The wonderful processes by which the entozoa 

 find their appropriate place of development, in all 

 their stages of growth, are analogous to this ; but are 

 too intricate for use here as illustrations. 



We have in the Bot-fly, another manifestation 

 of Instinct, that is difficult to be reconciled with 

 that theory which resolves it into fixed habits form- 

 ed by the experience of past generations ; or to 



