" Natural Selection " 65 



prey. The suppression of movement in the victim is the 

 only means of realising these conditions, and this 

 suppression to be complete requires sundry dagger 

 thrusts, one in each nerve centre. If the paralysis 

 and the torpor be not sufficient, the grey- worm will defy 

 the efforts of the huntress, will struggle desperately 

 on the journey, and will not reach the destination ; 

 if the immobility be not complete, the egg fixed at a 

 given spot on the worm will perish under the con- 

 tortions of the giant. There is no mean admissible, 

 no half-success. Either the caterpillar is treated 

 according to rule and the wasp's family is perpetuated, 

 or else the victim is only partially paralysed and the 

 wasp's offspring dies in the egg. 



" Yielding to the inexorable logic of facts, we will 

 therefore admit that the first sand-wasp on capturing 

 a grey-worm to feed her larva operated on the patient 

 by the exact method in use to-day. She seized the 

 animal by the skin of the neck, stabbed it underneath, 

 opposite each of the nerve centres, and if the monster 

 threatened further resistance munched its brain, for 

 an unskilled murderess, doing her work in a perfunctory 

 and haphazard fashion, would leave no successor, as 

 the rearing of the egg would become impossible. Save 

 for the perfection of her surgical powers, the slayer of 

 fat caterpillars would die in the first generation. What 

 chance has the operator of striking that one particular 

 spot were her lancet wielded without method ? The 

 chance is ludicrous. It is one against the countless 

 number of points whereof the caterpillar's body is 

 made up. And yet, according to the theorists, it is on 

 this chance that the sand-wasp's future depends. 

 What an edifice to balance on the point of a needle ! 

 . . . The egg, laid on its (the larva's) flank then, will 

 develop without risk. It is at most but a half of what 

 is absolutely necessary. Another egg is indispensable 



