INTRODUCTION. 1 5 



other spots for the dart to penetrate, because here is 

 the Ammophila, a near relative of the Sphex, which 

 chooses for its prey a caterpillar. It is free to in- 

 troduce its sting into any part of the body, and yet 

 with extreme certainty it strikes the two ganglions 

 already mentioned.i 



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 con- 

 sequence 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 pos- 

 sible ; 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 Bem- 

 bex, 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 larvK ; the corpses would putrefy. 



^ P. Marchal, " Observations sur P Amtnophila affinis" Arch, de 

 Zool. exfir. et genlr., ii. Serie, t. lo, 1892. 



