Chap. VIIL] OF NATURAL SELECTION. 361 



size, but in their organs of vision, yet connected bj 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 

 more and more of the smaller workers, until all the 

 workers were in this condition; we should then have 

 had a species of ant with neuters in nearly the same 

 condition as those of Myrmica. 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 confidently did I 

 expect occasionally to find gradations of important struc- 

 tures between the different castes of neuters in the same 

 species, that I gladly availed myself of Mr. F. Smith's 

 offer of numerous specimens from the same nest of the 

 driver ant (Anomma) of West Africa. The reader will 

 perhaps best appreciate the amount of difference in these 

 workers, by my giving not the actual measurements, 

 but a strictly accurate illustration : the difference was 

 the same as if we were to see a set of workmen building 

 a house, of whom many were five feet four inches high, 

 and many sixteen feet high ; but we must in addition 

 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 teeth. 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 tins latter 



