160 THE EVOLUTION THEORY 



complete liberation of the instinct is only effected by the visual 

 impression of the under side of the leaf. We cannot but be 

 astonished that there is room for such finely graded nerve-mechanisms 

 in the little brain of a butterfly, and yet it would be easy enough to 

 adduce still more complex instincts connected with oviposition in 

 insects. The large water-beetle, Hydrophilus piceus, lays its eggs on 

 a floating raft made by itself ; the gall-wasps must first pierce with 

 their ovipositor into a particular part of a particular plant to be able 

 to lay the eggs in the proper place, and this in no haphazard way but 

 with great carefulness and in a perfectly definite manner. But there 

 is no necessity to refer here to many or to the most complicated 

 cases of egg-laying ; I only wish to show that, even in the simple 

 cases, such as that of the butterflies just referred to, there is 

 a precisely regulated combination of actions which is executed 

 mechanically, and which cannot be interpreted as inherited habit, 

 because it never was a habit in airy individual of any generation. 



It is thus placed beyond the possibility of doubt that very many 

 instincts, at least, must depend on selection, and it would be useless 

 to go further in this direction by extending our survey to other 

 groups of instincts. I shall, however, return later on to the study of 

 instincts, and, after we have become acquainted with the main 

 features of the laws of inheritance, it will then be seen that, even 

 among higher animals, instincts can never be interpreted in terms of 

 the Lamarckian principle. 



