INSTINCT 215 



conclude from the analogy of ordinary variations, that 

 each successive, slight, profitable modification did not 

 probably at first appear in all the individual neuters in 

 the same nest, but in a few alone ; and that by the 

 long-continued selection of the fertile parents which 

 produced most neuters with the profitable modification, 

 all the neuters ultimately came to have the desired 

 character. On this view we ought occasionally to find 

 neuter-insects of the same species, in the same nest, 

 presenting gradations of structure ; and this we do find, 

 even often, considering how few neuter-insects out of 

 Europe have been carefully examined. Mr. F. Smith 

 has shown how surprisingly the neuters of severa] 

 British ants differ from each other in size and some- 

 times in colour ; and that the extreme forms can 

 sometimes be perfectly linked together by individuals 

 taken out of the same nest : I have myself compared 

 perfect gradations of this kind. It often happens that 

 the larger or the smaller sized workers are the most 

 numerous ; or that both large and small are numerous, 

 with those of an intermediate size scanty in numbers. 

 Formica flava has larger and smaller workers, with 

 some 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 intermediate con- 

 dition. So that we here have two bodies of sterile 

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

 but in their organs of vision, yet connected by some 

 few members in an intermediate condition. I may 

 digress by adding, that if the smaller workers had been 

 the most useful to the community, and those males and 

 females had been continually selected, which produced 



