We cannot suppose that the insect has anatomical and physiological knowledge to inform it of what it is doing. The act is distinctly instinctive, and seems imprinted by a fatality involving no possible connection with intelligence. But let us suppose that the ancestors of these Hymenoptera have thus attacked crickets and killed (not paralysed) them with one or more wounds at any point. By chance some of these insects, either in consequence of their manner of attacking the prey or from any other cause, happen to deliver their blows at the points in question. Their larvae on this account are placed in more favourable conditions than those of their relatives whom chance has less well served; they will prosper and develop sooner. They inherit this habit, which gradually becomes through the ages that which we know. It is possible; but why, it may be asked, this hypothesis, apparently gratuitous, of strokes of the sting given at random? Are there any facts which render this explanation plausible? Assuredly. Thus the _Bembex_, which especially attacks Diptera to make them the prey of its larvae, throws itself suddenly on them and kills them with one blow in any part of the body. It is unable in this way to amass in advance sufficient provision for its larvae; the corpses would putrefy. It is obliged to return from time to time bearing new pasture.[9] Again, M. Paul Marchal, taking up the study of instinct in the _Cerceris ornata_,[10] has shown that in this species at least of _Sphegidae_ the stings have not so considerable an effect. This insect attacks a wild bee, the _Halictus_. He strikes his victim with two or three strokes of the sting beneath the thorax, but the paralysis is not definite, perhaps on account of the nature of the venom, which is not identical in all species. The tortured creature may regain life at the end of some hours. Thus the _Cerceris_ is obliged to destroy the upper part of the neck by repeated malaxation of that part for several minutes at a time. The effect of this second act, by injuring the cerebroid ganglia, is to render impossible the return of action; moreover, it permits the aggressor to satisfy personal gluttony, and to feed on the liquids of the organism of the vanquished, which is easy, because the dorsal blood-vessel passes at this level. It can thus satisfy a personal need while thinking of the future of the race. [9] J. H. Fabre, _Souvenirs entomologiques_, pp. 225 _et seq._ [10] "Etude sur l'Instinct du _Cerceris ornata_," _Archives de Zoologie experimentale_, ii. Serie, t. 5, 1887. It has been said in this connection that in such cases the sure instinct with which these species were originally endowed has been distorted, but that is to admit some degree of variation; the hypothesis of degeneration is as gratuitous as the other, and if we go so far as to risk a hypothesis, it would be better to use it to explain facts and not to entangle them.