I20 THE INDUSTRIES OF ANIMALS. 



development is completed, with extremely interesting 

 details with which we need not now concern our- 

 selves. The larva of Sitaris is then in conditions 

 exceptionally favourable for growth ; but, in spite 

 of appearances, there is no reason for admiring the 

 marvellous foresight and extraordinary sureness of 

 instinct ; nearly everything depends on a fortuitous 

 circumstance, a chance. This becomes very evident 

 if we study another related beetle ; it is called 

 the Sitaris colletis, and lives at the expense of the 



Fin. 15. 



hymenopterous Colletes, as its relative at the 

 expense of the Anthopkbra. But these two species 

 of the same genus are very unequally aided by 

 chance. The one whose history we have just traced 

 attaches itself to an insect whose egg floats above a store 

 of honey ; the second chooses a victim who attaches 

 its egg to the walls of a chamber. (Fig. 15.) This 

 almost insignificant difference has a considerable 

 influence on the parasite's evolution. In the first case 

 it is alone, and may develop with certainty ; in the 

 second, on the contrary, several Sitaris penetrate the 



