Alone the female sphex engages in her terrible and clever strife with the cricket, whom she paralyzes with three stabs of her dagger in his three moto-nervous centres; alone she hollows the oblique burrow at the bottom of which live her larvæ; alone she adorns it, fills it with provisions, closes it. Alone the female cerceris heaps up in the deep gallery the stunned weevils and burn-cows, fruit of her excavations, larder for her progeny. Alone the she-osmie, she-wasp, she-philanthe--one would have to cite nearly all the hymenoptera. One understands better, when the insect deposits her eggs by chance, without prefatory manœuvres, or by special instruments, that the male co-operation is lacking; only the female cicada can sink her clever burrow in the olive bark. There are however couples among insects. Among coleoptera there are the "purse-maker," the necrophore. Stercorian geotrupes, lunar copris, onitis bison, sisyphus, work soberly side by side preparing the larder for their coming families. In these cases, the male seems master, he directs the manœuvres in the complicated operations of the necrophores. A couple get busy about a corpse, say of a field mouse; nearly always one or two isolated males join them, the troop is organized, one sees the chief engineer explore the territory and give orders. The female awaits them, motionless, ready to obey, to follow the movement. As soon as there is a couple the male necrophore commands. The male assists the female during the work of arranging the cell and the laying. Most purse-makers, sisyphus or copris make and transport together the pill which serves as food for the larvæ; their couple is just like that of birds. One might believe that in this case monogamy is necessitated by the nature of the work; not at all: the male in other quite closely related species, sacred scarab, for example, leaves the female alone to build the excremental ball in which she encloses her eggs. Coming up to vertebrata one finds also certain examples of a sort of monogamy: when the male fish serves as hatcher for his own eggs, either carrying them in a special pouch, or heroicly sheltering them in his mouth. This is rare, since, usually, the two sexes of fish do not approach each other, do not even know each other. Batrachians, on the contrary, are monogamous; the female does not lay save under male pressure, and it is so slow an operation, preceded by such long manœuvres that the whole season is filled with it. The male of the common land toad rolls the long chaplet of eggs about his feet as soon as it is divided, and goes in the evening to place it in the neighbouring pool. Nearly all saurians seem also to be monogamous. The he and she lizard form a couple said to last several years. Their amours are ardent, they clasp each other closely belly to belly.