300 MENTAL EVOLUTION OF ANIMALS. 



cricket, the insect is thrown, as in the previous case, upon its 

 back, and while holding it down with her mandibles firmly 

 fastened upon the last segment of its abdomen, her feet on 

 the sides holding down the body of the cricket — the anterior 

 feet holding down the long posterior legs of the prey, and the 

 hind feet holding back the mandibles, so as to prevent these 

 from biting, and at the same time making tense the mem- 

 branous junction of the head with the body — the Sphex darts 

 her sting successively into three nerve-centres ; first into the 

 one below the neck which she has stretched back for the pur- 

 pose, next into the one behind the prothorax, and lastly into 

 the one lower down. A cricket thus paralyzed will live for 

 six weeks or more. When the prey is a caterpillar, a series 

 of six to nine stings are given, one between each of the seg- 

 ments of the body beginning from the anterior end; the 

 brain is then partially crushed by a bite with the man- 

 dibles.* 



Now so far as the spider and the beetle are concerned, I 

 do not see much difficulty presented by the facts to our 

 theory of the formation of instincts. For as both the large 

 nerve-centres of the Spider and the sting of the Sphex occur 

 upon the median line of their respective possessors, if the 

 stinging of the ganglion were in the first instance accidentally 

 favoured by this coincidence — which appears to me not im- 

 probable, seeing that the nerve-centre is thus the most likely 

 place for the sting to strike, — it is evident that natural selec- 

 tion would have had excellent material on which to work for 

 the purpose of developing such an instinct as we now observe. 

 Again, in the case of the beetle, M. Fabre expressly notices 

 that the only vulnerable point in the hard casing of the 

 animal is in the articulation where the Sphex thrusts her 

 sting ; so that there is nothing very remarkable in natural 

 selection having developed an instinct to sting at the only 

 place in the body of the prey where stinging is mechanically 

 possible. 



But the case is certainly very different with the cricket 

 and the caterpillar ; for here — or at least in the latter case — 

 we encounter the extraordinary and unavoidable fact of an 

 insect, without any accidental guiding or mechanically 



* All the above facts are taken from the works of M. J. H. Fabre 

 (Souvenirs Entomologtques, 1870 and 1883), who was the first to observe and 

 describe them. 



