94 THE AMERICAN NATURALIST. [Vor. XXXVI. 
fact that he seems to have been much interested in ant archi- 
tecture, and has devoted no less than thirty-five pages to a 
presentation of this feature. It does not seem to have occurred 
to him that the character of the architecture of molifactens 
must be profoundly affected by two factors, — the nature of 
the soil and the age of the ant colony. Gravel-cone nests can, 
of course, be built only in soil that abounds in small pebbles, 
whereas nests dug in a uniform soft, loamy soil, like that of 
northern Texas along the Red River, must be simple disks or 
very low mound nests, as the soil brought up by the ants is 
spread out by the rains and the movements of the ants them- 
selves. On the other hand, a small, incipient colony of ants 
is unable to clear away much of the vegetation about the 
entrance to the nest. At least the tougher plants, like the 
grasses, whose hard siliceous stems offer considerable resistance 
to the mandibles of the ants, cannot be cut away till the colony 
waxes strong both in the size and number of its individuals. 
Then the work proceeds rapidly, the circular area coéxtensive 
with the subterranean galleries is completely cleared and 
opened up to the sun's light and warmth. This clearing is 
evidently an adaptation for insuring the greatest possible dry- 
ness in the granaries 
of the nest. The 
circular denuded disk 
or mound enlarges 
slowly year after year, 
and it should be noted 
that during this pro- 
Fic. 6. — Pogonomyrmex subdentatus Mayr. Worker. S ressive enlarg ement 
even the peripheral 
circle of ant rice is quite as ruthlessly cut down and cleared 
away along its inner edge as any other plants that may cast a 
shadow on the disk, and thereby enable the soil to retain the 
moisture. 
While we possess the observations of Buckley (61), Lince- 
cum ('62, '66, '74), and McCook (79), on the habits of the Texan 
P. molifaciens, of Mrs. Mary Treat (77) and McCook (79) on 
the * Florida harvester” (P. badius Latr.), and of McCook (82) 

