INSTINCT 887 



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 divided 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 different: 

 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, supplying the place of that excreted by the 

 aphides, or the domestic cattle as they may be called, 

 which our European ants guard and imprison. 



It will indeed be thought that I have an overweening 

 confidence 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 anal- 

 ogy 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 advantageous 

 modification, all the neuters ultimately came to be thus 



