GENERAL CONSIDERATIONS 365 



times the inability when she leaves the nest or prey so 

 suddenly that no study of the landmarks can be made, 

 again demonstrate place-memory. 



Odynerus geminus usually fills up her burrow solid with 

 mud, but on one occasion when danger threatened, she re- 

 moved enough mud from her chimney barely to seal the 

 cell below and then placed a thin layer of mud flush with 

 the surface of the earth. The time was too short for the 



A little piece of paper pinned to the ground to assist us 

 in finding the nest of O. geminus proved soon to be a land- 

 mark for this mother. After a few days we removed the 

 scrap of paper; the mother could not find the nest until the 

 paper was replaced. 



Odynerus dor sale, in going for water, follows landmarks. 

 One individual repeatedly flew to the railroad track, trav- 

 elled parallel to it for a short distance, then back in the di- 

 rection from which she came to her pool. The railroad 

 track was undoubtedly associated in her mind with the 

 direction of her flight. 



Fabre lays much stress upon the fact that Bembix will 

 stupidly tolerate dipterous parasites about the nest when 

 she has the power to dispose of them. But Stizus unicinc- 

 tus is not so slow, for she was able to recognize at a 

 glance the infestation of the hopper in the Priononyx 

 hole and fled from the place without laying her egg. 



An Arachnophoctonus ferrugineus dragging her prey 

 left it several times, to fly to the old log house some distance 

 away, and then returned very directly to her spider. She 

 undoubtedly travelled from the spider to the walls so often 

 to ascertain if she was going in the right direction, since 

 eventually the nest was made between its logs. 



In Priocnemis pompilus the instinct to enter the hole each 

 time before bringing in the spider was strong, despite the 

 fact that it meant disaster to do so, for the ledge before her 



