l6 THE INDUSTRIES OF ANIMALS. 



It is obliged to return from time to time bearing 

 new pasture.^ Again, M. Paul Marchal, taking up 

 the study of instinct in the Cerceris ornata^ has 

 shown that in this species at least of SphegidcB 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 impos- 

 sible 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. 



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. 



Plan of study of the various industries. — The 

 different industries carried on by animals may be 

 divided into a certain number of groups. In the case 



^ J. H. Fabre, Souvenirs entomologiques, pp. 225 ei seq. 

 ^ "Etude sur I'lnstinct du Cerceris ornaia," Archives de Zoologie 

 expMinentale, ii. Serie, t. 5, 1887. 



