364 SriMABY. [Chap. Yin. 



slight modifications of instinct which are in any way 

 useful. In many cases habit or use and disuse have 

 probably come into play. I do not pretend that the 

 facts given in this chapter strengthen in any great 

 degree my theory ; but none of the cases of difficulty, 

 to the best of my judgment, annihilate it. On the 

 other hand, the fact that instincts are not always 

 absolutely perfect and are liable to mistakes : — that no 

 instinct can be shown to have been produced for the 

 good of other animals, though animals take advantage 

 of the instincts of others ; — that the canon in natural 

 history, of " Xatura non facit saltuin," is applicable to 

 instincts as well as to corporeal structure, and is plainly 

 explicable on the foregoing views, but is otherwise 

 inexplicable, — all tend to corroborate the theory of 

 natural selection. 



This theory is also strengthened by some few other 

 facts in regard to instincts ; as by that common case of 

 closely allied, but distinct, species, when inhabiting 

 distant parts of the world and living under consider- 

 ably different conditions of life, yet often retaining 

 nearly the same instincts. For instance, we can under- 

 stand, on the principle of inheritance, how it is that the 

 thrush of tropical South America lines its nest with 

 mud, in the same peculiar manner as does our British 

 thrush ; how it is that the Hornbills of Africa and India 

 have the same extraordinary instinct of plastering up 

 and imprisoning the females in a hole in a tree, with 

 only a small hole left in the plaster through which the 

 males feed them and their young when hatched ; how 

 it is that the male wrens (Troglodytes) of North America 

 build u cock-nests," to roost in, like the males of our 

 Kitty- wrens, — a habit wholly unlike that of any other 



