cover all the phenomena alike? Finally let us take the case of the slave-owning ‘Amazon’ ants, _Polyergus rufescens_. Here we have a case which at the first blush looks like a perfect picture of an evolutionary process conducted on the principles of Lamarck’s theory. These ants, it may be supposed, were originally of the ordinary type of that industrious and respectable insect, but they were led by the weakness of some of their neighbours of another species to make occasional attacks on them for the purpose of carrying off their immature brood, the _pupæ_, as food. Some of these _pupæ_, near maturity at the period of their capture, would come out while stored-up in the nest of the conquerors, and when they did so would immediately set about doing the household work of the hive as if they were at home. _Polyergus rufescens_ ultimately became aware that a life of aristocratic leisure awaited him if he only captured enough _pupæ_ of another species of ant to do his work. He accordingly confined himself entirely to piratical expeditions of this nature, and in the course of time underwent a moral and physical transformation of a most remarkable kind. The ordinary ant instincts have disappeared in this variety. They do not make their nests, they do not gather stores, they do not mind their young, they do not even feed themselves—an Amazon ant will perish of starvation in the presence of food if there is not a slave ant to put it into his mouth. But they fight ferociously in their slave-raids, and the form of their mandible has changed to suit their mode of life. It has become a pair of sabre-like nippers, excellent for slaying a foe, but ill-adapted for carrying objects and other industrial occupations. Corresponding changes have taken place in the head and in the chitinous and muscular structure. We have before us, then, what would seem to an uninformed observer, a striking picture of the acquirement of a certain bodily form and a certain set of instincts by use, and the total loss of other traits by disuse, and of the fixing of these characters in a species by heredity. Yet the picture is altogether an illusion. However we are to explain the facts—of which more anon—we cannot do so by Lamarckism, for the simple reason that the peculiar instincts and bodily structure of the Amazon ants are confined to the so-called ‘worker,’ or in this case ‘soldier,’ caste, which are sexless, and incapable of reproducing their kind. If these were the individuals which originally started the slave system among the species, they could not possibly have transmitted the modifications, moral and physical, which they acquired. The queen-ants, which normally are the only fertile ants, transmit them, but do not possess them, and neither do the drones.