216 ON THE ORIGIN OF SPECIES 



more and more of the smaller workers, until all the 

 workers had come to be in this condition ; we should 

 then have had a species of ant with neuters very nearly 

 in the same condition with 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 to find gradations in important points of struc- 

 ture 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 measure- 

 ments, but a strictly accurate illustration : the differ- 

 ence 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 

 suppose that the larger workmen had heads four in- 

 stead of three times as big as those of the smaller men, 

 and jaws nearly five times as big. The jaws, more- 

 over, 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 this latter point, as 

 Mr. Lubbock made drawings for me with the camera 

 lucida 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 ; 



