CuAr. YII. OF NATURAL SELECTION. 229 



neuter insects, presenting gradations of structure ; and this we 

 do find, even frcquenth'-, considering liow few neuter insects 

 out of Europe have been carefully examined, ^[r. F. JSinith 

 lias shown that the neuters of several British ants differ sur- 

 ])risingly from each other in size, and sometimes in color ; and 

 that the extreme forms can be linked together by individuals 

 taken out of the sanu; nest ; I have myself compared j^erfect 

 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, while those of an interme- 

 diate size are scanty in numbers. Formica flava has larger and 

 smaller workers, with some few of intermediate size ; and, in 

 this species, as Mr, F. Smith has observed, the larger workere 

 have simj)lc eyes (ocelli), which though small can be plainly 

 distinguished, whereas the smaller workers have their ocelli 

 rudimentary. IlaWng carefully dissected several specimens ot 

 these workers, I can affirm that the eyes are far more rudimen- 

 tary 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 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, yet 

 conn(^cted by some few members in an intermediate condition. 

 I may digress by adding, that if the smaller Avorkers had been 

 the most useful to the community, and those males and females 

 had been continually selected, which produced more and more 

 of the smaller workers, until all the workers were in this condi- 

 tion, we should then have had a species of ant with neuters 

 nearly in the same condition with those of Mynnica. For the 

 workers of Mynnica have not even rudiments of ocelli, though 

 the male and female ants of this genus have Avcll-develoi)ed 

 ocelli. 



I may give one other case : so confidently did I expect to find 

 gradations in important points of structure between the differ- 

 ent castes of neuters in the same species, that I glaiUy availed 

 myself of Mr. F. Smith's offer of numerous specimens from the 

 same? nest of tlie driver-ant (Aiiomma) of West Africa. The 

 reader will peihajis best a]i])reciate the amount of difference in 

 these workers, by my giving not the actual measurements, but 

 a strictly aecurate illustration : the difference was the same as 

 if we were to sec a set of workmen building a house, of whom 

 many were five feet four inches high, and many sixteen feet 



