32 
Psyche 
[ March 
the occurrence of temperature fluctuations, (fig. 2). In 
most cases the brood is isolated in separate chambers ac- 
cording to age but often it is intermingled in the same 
chambers. 
The twigs and grasses which comprise the external archi- 
tecture also extend into the ground for a distance of from 
several inches to a foot and rest on a crateriform base. 
Perhaps this provides anchorage for the mound or even 
aeration of the brood. The slight precipitation occurring 
Fig. 2. Diagrammatic longitudinal section of a mound of F. ob- 
scuripes. Twin Falls, Idaho. A, a main gallery; B, auxil- 
iary chamber; C, main brood chamber. 
in the West has little effect on the mounds and there is 
no great danger of the crateriform base filling up with 
water. 
Colonies of obscuripes are always quite populous and in- 
clude both major and minor workers. Both of these aid 
in the protection of the colony, ejecting formic acid at the 
slightest unnatural disturbance. The macrogynous queens 
in a single colony vary in number, there always being two 
