Chap. Vin.] OF NATURAL SELECTION. 361 



nest, differing not only in size, but in their organs of 

 vision, yet connected by some few members in an inter- 

 mediate condition. I may digress by adding, that if the 

 smaller workers had been the most useful to the com- 

 munity, and those males and females had been continu- 

 ally selected, which produced more and more of the 

 smaller workers, until all the workers were in this con- 

 dition; we should then have had a species of ant with 

 neuters in nearly the same condition as those of Myr- 

 miea. For the workers of Myrmica have not even rudi- 

 ments 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 ex- 

 pect 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 measure- 

 ments, 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, 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 dif- 

 ferent sizes, yet they graduate insensibly into each 

 other, as does the widely-different structure of their 



