honey, it partakes of it, and then the 'mistress' comes and strokes the 'slave' with her antennæ to signify her desires, whereupon the 'slave' proceeds to feed her from its own crop. [17] 'New' in this sense, that the instinct is not exhibited by most worker-ants, that it did not occur in the primaeval ancestors of modern ants. It is, however, exhibited by a number of modern forms, and even by some German species. But while the _Polyergus_ workers have forgotten their domestic habits, and have even ceased to be able to recognize their food, remarkable changes have taken place in their jaws; these have lost the blunt teeth on the inner margin, which, in other species, serve for masticating the food, for seizing building material, and for other domestic occupations, and have become sharp weapons, bent in the form of a sabre, very well suited for piercing the head of an enemy, but also well adapted for carrying off the pupæ, because they can seize them without doing them any injury. No one will doubt that the predatory expeditions of the Amazon ants, and the slave-making habit, can only have developed after the habit of living in large companies had long existed, and this case proves that variations of instinct, as well as of bodily structure, can take place even after the workers have long been sterile. The case is the more instructive that it _seems_ as if it were due to the transmission of a newly acquired and inherited habit of life, while in point of fact these Amazon-workers can transmit nothing, because they bear no offspring. But if old instincts can be lost, and new ones acquired, when all possibility of inheritance is excluded, we see that Nature has no need of the Lamarckian factor of modification for her transformations and new adaptations.