large and small are numerous, with those of an intermediate size scanty
in numbers. Formica flava has larger and
smaller workers, with some of intermediate size; and, in this species,
as Mr. F. Smith has observed, the larger workers have simple eyes
(ocelli), which though small can be plainly distinguished, whereas the
smaller workers have their ocelli rudimentary. Having carefully
dissected several specimens of these workers, I can affirm that the
eyes are far more rudimentary in the smaller workers than can be
accounted for merely by their proportionally lesser size; and I fully
believe, though I dare not assert so positively, that the workers of
intermediate size have their ocelli in an exactly intermediate
condition. So that we here have two bodies of sterile workers in the
same nest, differing not only in size, but in their organs of vision,
yet connected by 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 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 structure 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 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 this latter point, as
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