primary constituent, possessing the power of developing into a queen under the influence of rich food and into a worker when poorly nourished, how could we explain the fact that in the latter case not only does degeneration of individual parts occur, but also a different and stronger development of other parts? It seems to me that on the grounds of the phenomena observable in the social insects alone, we have no choice but to accept the theory of ids; for only by its means does it become intelligible how totally opposite characters can be brought forth by the stimulus of poverty of food—degeneration of the ovaries, the receptaculum, and the wings, and frequently a reduction of the entire bulk of the body on the one hand; and on the other, increase and higher differentiation of individual parts, such as the brain in worker-ants and the head and the jaws in the soldiers, together with many correlated instincts. None of these variations,—not even the frequently striking small size of the workers,—originates owing to the direct action of poor food. Should we attempt to make dwarfs of any insect by starvation during the course of development, we should at most get a reduction to about half the normal size: this was occasionally the case with the butterflies and flies referred to above.
But the workers of some ants (Atta fervens) are ten times smaller than the fertile females; and even if a small proportion of this difference is to be ascribed to a phyletic enlargement in the females, a considerable part must without doubt be credited to a diminution in the workers. Eméry is therefore so far right in his
