In the substance of those beautiful leaves of the water-lily which cover our ponds in summer, we often see a charming insect, known by the name of _Agrion virgo_, or damsel dragon-fly, a name given to it on account of its graceful attitudes and its elegant appearance. We observe this insect deposit its eggs with great prudence, fully persuaded that they are safe in the midst of the water; but the poor neuroptera reckons without its host. An hymenopterous insect, named _Polynema_, is there, watching every movement of the Agrion; and as soon as the latter has laid an egg, the Polynema darts down like a bird of prey on its victim, pierces it, and deposits its own egg in the interior. The egg of the wounded agrion will hatch a polynema. The cuckoo acts with less cruelty, since she is contented to lay her eggs 170 by the side of those which occupy the nest. Remarkable examples of the refinement of cruelty and of gluttony are to be found in this little animal world. It is not enough that some among them feed on the entrails of their young neighbours; there are wasps which, in order to make the agony last longer, place by the side of the eggs which they lay, chloroformed flies, which wait patiently for the time when they can yield themselves up, still palpitating, to these young tyrants. The days, the hours, perhaps even the minutes, are scrupulously reckoned for the preparation of this living morsel. As the process of hatching proceeds, the repast acquires properties more and more adapted to the age of the young wasps. The _Sphex_ is not less cruel. Some of the insects which are found in South America attack, not the young ones, but those which are grown up, and snatch spiders from their webs as slave-hunters carry off negroes from the wood; they garotte them, and cram them into narrow cells, after having chloroformed them to preserve them more effectually. These spiders, retaining enough life not to lose their nutritious qualities, become the easy prey of the larvæ of the Sphex. The mother of these hymenoptera takes care to deposit her eggs, as well as the living booty, in such a manner that the larvæ, at the moment of being hatched, live in abundance. These young larvæ, white and without feet, are dainty enough to reject any other kind of food. This is an act of cruelty which resembles that of the ichneumon, to which it may well be compared. The _Platygasters_, another kind of hymenopterous insects, show their cruelty in a different manner; they live in the bodies of the larvæ 171 of _Cecidomyæ_ which are lodged in the rolled leaves of the Salix, and suck the blood of their victims. Other insects, known by the name of _Meloïdeæ_, adopt a different plan. Their larvæ have been long known by the name of _bee-lice_; but they had not been recognized in the perfect state, as the larvæ did not resemble their parents.