Wallace opposed Darwin's theory of sexual selection, but it can scarcely be said that his attitude toward it bears critical examination. On the one hand, as has already been noted, he saw but one side of that theory and that the unessential side, and, on the other hand, his own view really coincided with the more essential elements in Darwin's theory. In his _Tropical Nature_ he admitted that the male's "persistency and energy win the day," and also that this "vigor and liveliness" of the male are usually associated with intense coloration, while twenty years later (in his _Darwinism_) he admitted also that it is highly probable that the female is pleased or excited by the male's display. But all that is really essential in Darwin's theory is involved, directly or indirectly, in these admissions. Espinas, in 1878, in his suggestive book, _Des Sociétés Animales_, described the odors, colors and forms, sounds, games, parades, and mock battles of animals, approaching the subject in a somewhat more psychological spirit than either Darwin or Wallace, and he somewhat more clearly apprehended the object of these phenomena in producing mutual excitement and stimulating tumescence. He noted the significance of the action of the hermaphroditic snails in inserting their darts into each other's flesh near the vulva in order to cause preliminary excitation. He remarks of this whole group of phenomena: "It is the preliminary of sexual union, it constitutes the first act of it. By it the image of the male is graven on the consciousness of the female, and in a manner impregnates it, so as to determine there, as the effects of this representation descend to the depths of the organism, the physiological modifications necessary to fecundation." Beaunis, again, in an analysis of the sexual sensations, was inclined to think that the dances and parades of the male are solely intended to excite the female, not perceiving, however, that they at the same time serve to further excite the male also.[24]