362 OBJECTIONS TO NATURAu bJiLBCTION. [Chap. VIII. 



jaws. I speak confidently on this latter point, as Sir J. 

 Lubbock made drawings for me, with the camera lucida, 

 of the jaws which I dissected from the workers of the 

 several sizes. Mr. Bates, in his interesting ' JSTaturalist 

 on the Amazons,' has described analogous cases. 



With these facts before me, I believe that natural 

 selection, by acting on the fertile ants or parents, could 

 form a species which should regularly produce neuters, 

 all of large size with one form of jaw, or all of small 

 size with widely different jaws; or lastly, and this is 

 the greatest difRculty, one set of workers of one size 

 and structure, and simultaneously another set of workers 

 of a different size and structure; — a graduated series 

 having first been formed, as in the case of the driver 

 ant, and then the extreme forms having been produced 

 in greater and greater numbers, through the survival of 

 the parents which generated them, until none with an 

 intermediate structure were produced. 



An analogous explanation has been given by Mr. 

 Wallace, of the equally complex case, of certain Malayan 

 Butterflies regularly appearing under two or even three 

 distinct female forms; and by Fritz Miiller, of certain 

 Brazilian crustaceans likewise appearing under two wide- 

 ly distinct male forms. But this subject need not here 

 be discussed. 



I have now explained how, as I believe, the wonder- 

 ful fact of two distinctly defined castes of sterile workers 

 existing in the same nest, both widely different from 

 each other and from their parents, has originated. We 

 can see how useful their production may have been to a 

 social community of ants, on the same principle that 

 the division of labour is useful to civilised man. Ants, 

 however, work by inherited instincts and by inherited 



