Chap. VII. 
NEUTEK INSECTS. 
241 
workers, by my giving not tbe 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 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- 
diflferent 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 dis¬ 
sected 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 cKmax 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 
M 
