378 



growth of the plant, in consequence of which the pupa, instead of 

 remaining under the water, was gradually lifted up two feet above 

 it and perished. * Insects also not unfrequently lay their eggs in 

 wrong places, where the larvae when hatched can get no suitable 

 food. The flesh-fly, attracted by the carrion smell, will deposit its 

 eggs in the flowers of the stinking Stapelia ; at another time, 

 where the eye or touch may direct it, but where the right odour 

 cannot exist, on a fui* cap. Kirby and Spence mention the case of 

 the common house-fly even laying its eggs in a snuff-box, the snuff" 

 being mistaken for dung, t 



In reference to the general subject of instincts it may be 

 remarked that they depend for the most part on the conditions of 

 the outer world as manifested in the particular locality in which 

 animals are placed. These conditions act diff"erently upon different 

 constitutions. If we suppose the conditions of a country changed, 

 the result will probably be that some species of animals who 

 cannot accommodate themselves to the change fall victims to it 

 and at once perish ; " others more or less affected may continue 

 through several generations, but with decreasing vigour, and die 

 out gradually ;" while all those who are suited to it, or who can 

 adjust their habits to meet the requirements of the case, thrive and 

 prosper. The adjustment may not be made at once, or completed 

 in the life time of an individual, but if at all successful, the 

 advantage arising from it will be inherited and improved by the 

 offspring, and each generation in this way will gain upon the one 

 that preceded it. The changes above supposed may arise from 

 various causes. There may be a change of climate, or a change 

 affecting the supplies of food, or the face of a country may be so 

 altered as to bring about the destruction of the fittest places for 

 rearing young, or the change besides being unfavoiu-able for some 

 of its old inhabitants may be favoiu-able to other species, strangers, 

 which come and live there, and which may be the natural enemies 

 of the former. But whatever the change may be, it is obvious 

 that unless an animal can accommodate itself to the new circum- 

 stances, or go elsewhere, which not all species have it in their 



* See Ent. Trans., 3rd Ser., vol. v., Proceed, pp. xiv., xv. 

 t Introd. to Eutomol., vol. ii., p. -ITl. 



