statement, involving, as it does, M. Maupas in a contradiction; for two pages before this he speaks of the mode of the appearance of copulation as in the epidemic form. All observers, he says, that have occupied themselves with this phenomenon, state that it is suddenly developed in the little aquariums in which the animals are contained, and very rapidly becomes general (page 41). To this then the divergences of fact are reduced—a matter entirely insignificant; and I believe it useless to dwell upon it longer. The question of interpretation remains. I shall also say a few words with reference to this, although the disagreement is at bottom not much more serious. We have seen, that, according to M. Maupas, the Infusoria do not seek each other and copulate until after a fast of considerable duration caused by exhaustion of the store of food in the medium in which they live. The author concludes from this that scarcity of food is the sole and real cause of the great agitation in which they are then seen. "When an infusion thickly populated begins to get exhausted, the animalcula congregate together, always forming those whitish cloud-spots that we have described as the prelude to copulation.... Not until afterwards do the actual movements of copulation occur, which never last very long." Accordingly, there is first an agitation produced by hunger, and only in consequence of that are the preliminaries of copulation brought about. Admitting this interpretation as exact, which is indeed a question that I reserve, I conclude that M. Maupas completely accepts the facts of the preliminaries of copulation, distinguishing them from other phenomena that precede them. He says, moreover, and these are his own words, that the sexual impulse does indeed exist in these little creatures. Unquestionably he is right in adding that this sexual impulse presents in the ciliate Infusoria manifestations much simpler than in the higher animals, and that it is otherwise in accord with their simplicity of organisation. That is evident, and no one I believe has ever maintained the contrary. Finally, the author refuses to admit that the sexual manifestations of the Infusoria can be compared with the phenomena of _rut_. "Rut," he says, "the external and psychic manifestations of which we know with any degree of exactitude only in mammals, is a reflex phenomenon concomitant with and consecutive to the maturation of the Graafian vesicles. It is therefore an especial phenomenon peculiar to the females of the highest group of the animal series. Males are not subject to rut, but are always ready to experience the sexual excitation whenever they find themselves in contact with females that are fallen into that condition" (page 414).