Why not pounce on it and get rid of it? The Bembex flies fast enough to overtake it, and, small as it is, the larvæ would not disdain it, since they eat all and every Diptera. Yet the Bembex flies in terror before an enemy which one bite would hew in pieces. I really feel as though I saw a cat wild with terror before a mouse. The ardent pursuer of Diptera is driven away by a Dipteron, and that one of the smallest! I bow before the facts without any hope of ever comprehending this reversal of parts. To be able to get rid easily of a mortal enemy, who is meditating the ruin of your family, and who might make a feast for them—to be able, I say, to do this, and not to do it when the foe is there, within reach, watching you, defying you,—is the height of folly in an animal. Folly, however, is not rightly the word: let us rather talk of the harmony of creatures, for since this wretched little Dipteron has its small part to play in the great whole of things, the Bembex must needs respect it and basely flee before it,—otherwise long ago there would have been no more Dipteron of this species in the world. Let us trace the history of this parasite. Among Bembex nests there are found, and that frequently, some which are occupied at the same time by the larvæ of the Hymenoptera and by other larvæ—strangers to the family and greedily sharing their food. These strangers are smaller than the nursling of the Bembex—shaped like a tear, and of the colour of wine, from the food paste which can be seen through their transparent bodies. Their number varies from six to ten or more. They belong to a kind of Dipteron, as may be perceived from their form and from the pupæ which one afterwards finds in their place. The demonstration is completed by bringing them up one’s self in a box, where, fed daily with flies, and laid on sand, they turn into pupæ, whence issue the following year little Diptera—Tachinids of the genus Miltogramma. This is the Dipteron which, when lying in wait near the burrow, awakens such alarm in the Bembex. Her terror is only too well founded. This is what happens in the dwelling. Around the heap of food which the mother wears herself out in providing in sufficient quantity, sit in company with the legitimate nursling from six to ten hungry guests, who put their sharp mouths into the general heap as unceremoniously as if they were at home. Concord seems to reign at table. I have never seen the legitimate larva take offence at the indiscretion of the strangers, nor observed these attempt to trouble its repast. All keep themselves together, and eat peaceably without annoying their neighbours.