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Show 240 INSTINCT. CHAP. VII. k . tl me of intermediate size ; and, ~mall~r wor .ers, WI 1 so ~ S ith has observed, tho m this species, as Mr. F. m . . larger wor k ers h ave SI' mple eyes (ocelli), whwh though smal1 can b e p1 a i.n l y distinguished, whereas the· smaller worl rers h ave thei·r ocelli rudimentary. Havin1g careI-fu lly di ssec t ed se Veral specimens of these . wor cers, . can a ffi rm tha t the eyes are far more rudimentary m the smaller workers than can ~e accounted for m~rely by their proportionally lesser si.z~ ; and I fully beheve, th h I dare not assert so positively, that the workers ofo inutge rmediate size have the·n oce III' I·n an exact ly I·n t ~r-di te condition. So that we here have two boches me a di£P . t nl . of sterile workers in the same nest, uenng no o yIn · but in their organs of vision, yet connected by some mz~ d' . I few members in an intermediate con ItiOn. may digress by adding, that if the smaller workers had been the most useful to the community, and tho~e males and females had been continually selected, which produced more and more of the smaller workers, until all the orkers had come to be in this condition ; we should ;_en have had a species of ant with neuters v~ry nearly in the same condition with those of My.rmiCa. For the workers of Myrmica have not even rudiments of ocelli, though the male and female ants of this genus have well-developed ocelli. . I may give one other case : so co~fidently did I expect to find gradations in important p~Ints of structure between the different castes of neuters In the same species that I gladly availed myself of Mr. F. Smith's ~ffer of ~umerous specimens from the same nest of the. dnve~ ant ( Anomma) of West Africa. The. reader ':ill pe:~ haps best appreciate the amount of difference In the workers, by my giving not the actual ~easuremen~~ but a strictly accurate illustration : the differenc~ V: the same as if we were to see a set of workmen buildmg CHAP. VII. NEUTER INSECTS. 241 a house of whom many were five feet four inches high, and many sixteen feet high ; but we must suppose that the larger workmen had heads four instead of three times as big as those of the smaller men, and jaws nearly five times as big. The jaws, moreover, of the working ants of the several sizes differed wonderfully in shape, and in the form and number of the tee~h. But the important fact for us is, that though the workers can be grouped into castes of different sizes, yet they graduate insensibly into each other, as does the widely-different structure of their jaws. I speak confidently on this latter point, as Mr. Lubbock made drawings for me with the camera Iucida of the jaws which I had dissected from the workers of the several sizes. With these facts before me, I believe that natural selection, by acting on the fertile parents, could form a species which should regularly produce neuters, either all of large size with one form of jaw, or all of small size with jaws having a widely different structure ; or lastly, and this is our climax of difficulty, one set of workers of one size and structure, and simultaneously another set of workers of a different size and structure ; -a graduated series having been first formed, as in the case of the driver ant; and then the extreme forms, from being the most useful to the community, having been produced in greater 'and greater numbers through the natural selection '"of the parents which generated them ; until none with an intermediate structure were produced. Thus, as I believe, the wonderful fact of two distinctly defined castes of sterile workers existing in the same nest, both widely different from each other and from the~ parents, has originated. vVe can see how useful the~r production may have been to a social community of Insects, on the same principle that the division of M |