48 PHIL RAU AND NELLIE RAU 



t 



case comes from her own body, hence the process is physiological, 

 while in the wasp, nidification plus provisioning is psychological 

 in its origin. 



Cells that were completed and sealed without provisions or egg 



One hundred seventy-six cells, or 4 per cent, of the total 

 number, were properly made but sealed empty. These were 

 made by 132 mothers, who erred in this frequency: 



132 176 



* 



Thus we see that it is an error which is committed occasionally 

 by many wasps (in this population 1 mother out of every 5) ; 

 but to a large extent by very few. The two cases of 4 and 6 

 empty cells to a nest were both in large nests, and of the many 

 one-celled nests in the collection only 2 were empty. In other 

 words, a mother frequently leaves one or two cells of her nest 

 empty, but rarely leaves her whole nest, be it large or small, 

 in that condition. In the nest of 36 cells, the largest in the 

 collection, as we cited before, the mother had sealed 17 of the 

 well-filled cells without the egg, but she had failed to provision 

 only one cell. Some other mothers built large nests without 

 even a single failure in this point. 



Number of cells unsealed 



We occasionally find cells which have been completed but 

 not sealed; they are sometimes quite empty and sometimes 

 partly filled. with spiders. The sight of a deserted cell partly 

 filled with provisions for the young at once suggests another 

 tragedy of the insect world, — a mother wasp who has met her 

 death while out foraging for her brood. But since the mother 

 can meet such a death only once to forever prevent her return 

 to her nest, and since we find some mothers having two to four 

 such cells, we must attribute at least part of these cases to some 

 other causes, such as forgetfulness, etc. There were 126 of 



