PHYLUM ARTHROPODA — CLASS INSECTA 337 



trying to cut it off. This is probably a part at least of the process 

 of paralyzing the victim. These paralyzed Pieridae larvae have 

 been kept in the laboratory in bottles for two weeks in warm 

 weather before there began to be any change in their appearance. 

 After that time they began to decompose rapidly. 



"After the cell is provisioned with the Pieridae larvae the female 

 attaches the egg to the upper part of the cell by a short hairlike 

 process 1.8 mm. in length with the point of attachment to the cell 

 wall concave and about 2 mm. in diameter. Only one egg is de- 

 posited in each cell. The cell is then sealed over by wetting the 

 soil at the surface and then carrying it down to be moulded into an 

 apparently air- and water-tight compartment. In order to observe 

 this process, the writer used a small pocket mirror to reflect the 

 light down into the hole. This did not seem to interfere with the 

 activity of the wasp. 



"Most of the nests observed in this study consisted of two cells, 

 with single-celled nests ranking second and three-celled nests third 

 in frequency. The writer was not successful in hatching out all the 

 individuals of any three-celled nest dug from the ground but those 

 containing one or two cells were often hatched successfully. Of 

 those individuals successfully reared in the laboratory it was found 

 that in the case of the one-celled nests the individual invariably de- 

 veloped into a female, while with the two-celled nests the larva in 

 the lower cell always developed into a female and the upper in- 

 dividual into a male. No successful observations were made on the 

 three-celled nests. The facts of the case would seem to indicate 

 that the male develops more rapidly than the female, since the egg 

 in the lower cell is laid before that in the upper cell. It was noted 

 that the wasp in the lower cell did not emerge until three days 

 after the top cell had been vacated. The above condition applies 

 primarily to two-celled nests, although it might be equally true of 

 the three-celled types. 



"It is evident from this study that the eggs laid in July and 

 August hatch and remain in a late larval instar throughout the 

 winter. On August 2 a number of larvae were collected and placed 

 in glass vials. During the warm weather they were kept moistened 

 by placing a few drops of water on blotting paper covering the 

 cells. About the middle of September they were placed in a north 

 room of the writer's home where they were left throughout the 



