Field Studies of the Non-Social Wasps 399 
top she had laid her floor. Below this were evidences 
of old mud partitions, showing that this mother was not 
the first to use the abode, but that she had adapted the 
ready-made tunnel to her needs. Even at this point it is 
possible to perceive the differences between this and the 
sister species, Odynerus (Stenodynerus) pennsylvanicus; 
these larvae seem larger, and the cauls or partial co- 
coons are larger; moreover this material looks more 
like silk spun from glands, probably in the mouth, 
whereas in the pupae of the other species it appears that 
the vestiges of cocoons are from material from the ali- 
mentary canal. Bits of this material from the nest of O. 
foraminatus, examined under the microscope, show silk- 
hke threads crossing and recrossing in every direction. 
I do think, too, that into this network the material from 
the alimentary canal is injected, as in Trypoxylon poli- 
tum and Chalybion caeruleum. The cocoon of O. pennsyl- 
vanicus, under the microscope, shows the same silky con- 
dition, excepting that, at least in my sample, the silken 
threads are fewer and the filling substance or varnish 
more plentiful. The cocoon of this species differs from 
that of O. pennsylvanicus also in that this material forms 
not only a cap, but also something which has the sem- 
blance of a cocoon extending under the body and some- 
times around the dorsal side. 
The partitions in this nest were made of mud and pos- 
sibly the remains of debris that the mother found in the 
tunnel, and also seemed to be made in two parts, as de- 
Seribed for O. pennsylvanicus. In the upper four cells 
of this series, these two walls forming each partition 
were very close together ; in the two lower ones, the space 
between the two layers was much greater, one measuring 
5/16 inch and the other %4 inch. 
