THE BIOLOGY OF THE MUD-DAUBING WASPS 47 



Assuming that each mother is responsible for one nest complete, 

 we find from this tabulation that 275 mothers built and pro- 

 visioned these 537 cells without laying their eggs therein, and 

 the number of times each mother proved "forgetful" in this 

 respect varied from 1 to 7 times, with the one exceptional case 

 of the largest nest in the whole collection, wherein she failed 

 to oviposit in 17 of them, about one half of the cells which she 

 made. It may be that this exceptional mother was favored 

 with extraordinary longevity and that even after her quota 

 of ova was exhausted her domestic instincts prompted her to 

 go on faithfully building and providing, even though the species 

 would derive no benefit from her labor. The table shows that 

 the greatest number of mothers erred in one or two of their 

 cells, but this is the natural sequel to the fact that a great major- 

 ity of the nests contain only a few cells. We sought for some 

 correlation between this parental tendency and the number of 

 cells in the nest, but we found none; the large and the small 

 nests were equally likely to suffer from this form of neglect. 

 The phenomenon seems to be largely a matter of individual 

 temperament. Frequently a handsome nest of many cells was 

 faultless in this respect, while sometimes a single cell, the only 

 domestic attempt of the mother, was a dismal failure because 

 she had failed in this vital point of depositing an egg in the 

 otherwise perfect nest. Only in rare cases was the mother 

 forgetful of her egg throughout her work (excepting in single- 

 celled nests) ; in almost all of the nests we got evidence of fertile 

 eggs in some of the cells. It was for a time thought that prob- 

 ably an infertile egg had been deposited and that this in its 

 shrivelled condition might have been overlooked, so a careful 

 search was always made for any evidence of such an egg, but 

 none was ever found. Since more recently we have watched 

 Mother Sceliphron fill and seal her cells without the egg, we 

 feel reasonably certain in attributing this condition to her 

 forgetfulness or her sterility, and not to infertility. We have 

 not ascertained to what extent the wasp is forgetful of laying 

 the egg, or to what extent this lack of egg-deposition is due 

 to sterility or infertility. If she be sterile or unfertilized, it is 

 even more strange that she should go on making and stocking 

 her cell than that the unfertilized mantis should continue to 

 make her egg-case, for in the mantis the material for the egg- 



