144 Evolution and Adaptation 



may be applied to the family, as well as to the individual, 

 and may thus give the desired end." 



Darwin did not fail to see that there is a further difficulty 

 even greater than the one just mentioned. He says: "But 

 we have not as yet touched on the acme of the difficulty ; 

 namely, the fact that the neuters of several ants differ, not 

 only from the fertile females and males, but from each other, 

 sometimes to an almost incredible degree, and are thus di- 

 vided into two or even three castes. The castes, moreover, 

 do not commonly graduate into each other, but are perfectly 

 well defined ; being as distinct from each other as are any 

 two species of the same genus, or rather as any two genera 

 of the same family. Thus in Eciton, there are working and 

 soldier neuters, with jaws and instincts extraordinarily dif- 

 ferent : in Cryptocerus, the workers of one caste alone carry 

 a wonderful sort of shield on their heads, the use of which 

 is quite unknown : in the Mexican Myrmecocystus, the 

 workers of one caste never leave the nest ; they are fed by 

 the workers of another caste, and they have an enormously 

 developed abdomen which secretes a sort of honey, supply- 

 ing the place of that excreted by the aphides, or the domes- 

 tic cattle as they may be called, which our European ants 

 guard and imprison." 



"It will indeed be thought that I have an overweening con- 

 fidence in the principle of natural selection, when I do not 

 admit that such wonderful and well-established facts at once 

 annihilate the theory. In the simpler case of neuter insects 

 all of one caste, which, as I believe, have been rendered 

 different from the fertile males and females through natural 

 selection, we may conclude from the analogy of ordinary 

 variations, that the successive, slight, profitable modifications 

 did not first arise in all the neuters in the same nest, but in 

 some few alone ; and that by the survival of the communities 

 with females which produced most neuters having the advan- 

 tageous modification, all the neuters ultimately came to be 



