Chap. VIII.] OF NATURAL SELECTION. 231 



different : in Cryptocerus, the workers of one caste alone carry n 

 wonderful sort of shield on their heads, the use of which is quitfc 

 unknown: in the Mexican Myrmecocystus, the workers of one 

 caste never leave the nest ; they are fed hy the workers of another 

 caste, and they have an enormously developed ahdomen which 

 secretes a sort of honey, supplying the place of that excreted hy the 

 aphides, or the domestic cattle as they may he 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 analogy of ordinary variations, that the successive, slight, pro- 

 fitable 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 characterised. According to this view we ought occasion- 

 ally to find in the same nest neuter insects, presenting gradations 

 of structure ; and this we do find, even not rarely, considering how 

 few neuter insects out of Europe have been carefully examined. 

 Mr. E. Smith has shown that the neuters of several British ants 

 differ surprisingly from each other in size and sometimes in colour ; 

 and that the extreme forms can be linked together by individuals 

 taken out of the same nest: I have myself compared perfect 

 gradations of this kind. It sometimes happens that the larger or 

 the smaller sized workers are the most numerous ; or that both 

 large and small are numerous, whilst those of an intermediate size 

 are scanty in numbers. Formica fiava has larger and smaller 

 workers, with some few of intermediate size ; and, in this species, 

 as Mr. F. Smith has observed, the larger workers have simple eyes 

 (ocelli), which though small can be plainly distinguished, whereas 

 the smaller workers have their ocelli rudimentary. Having 

 carefully dissected several specimens of these workers, I can affirm 

 that the eyes are far more rudimentary in the smaller workers than 

 can be accounted for merely by their proportionally lesser size ; and 

 I fully believe, though I dare not assert so positively, that the 

 workers of intermediate size have their ocelli in an exactly inter- 

 mediate condition. So that here we have two bodies of sterile 

 workers in the same nest, differing not only in size, but in their 

 organs of vision, yai connected by some f3w members in an inter- 



