210 THE SOLITARY WASPS. 



search of new prey.* After two successive trips she penetrated 

 a third time into her dwelling and began to reject the dry sand 

 which had been thrown in. In the midst of this sand was a 

 bee. It was evident that in one of the trips that we had seen 

 her make she could not reach directly to the cell which she 

 was provisioning and dropped the victim at the place where she 

 had to stop. Presently the wasp flew away. The hours passed 

 on, and she returned without a bee, entered and threw out the 

 other one which she now considered an encumbering object. 

 Thus of two victims which were procured with great trouble, 

 one was abandoned on the threshold, and the other was dropped 

 half way in neither served as food for larvae. What of that? 

 Cerceris had given the sting that was enough. 



At another time a nest, one of the cells of which was not en- 

 tirely provisioned, was destroyed at evening. On the next 

 morning Cerceris brought a newly stung bee and placed it in 

 the hole. On the following day she came again, charged with 

 prey, and dropped her bee which rolled to the bottom of the ex- 

 cavation. She had not brought the full number for provision- 

 ing the nest. Instinct commanded her to bring them, and she 

 obeyed, but not knowing where to put them, let them fall. 



These things show the astonishing force with which a habit, 

 once acquired, fixes itself in the brain of an insect, and is trans- 

 mitted from generation to generation. It is precisely this which 

 constitutes instinct and it is difficult to see how these facts can,, 

 as some authors would wish, make us believe that insects are 

 incapable of acquiring habits, which, growing stronger and 

 stronger, are substituted little by little for old ones. In a word, 

 it is difficult to see how any one can find in them any proof of 

 immutability of instinct. 



*Our P. punctatus, under similar circumstances, dropped the bee 

 while she cleared the entrance but then picked it up and took it in. 



