446 THE AMERICAN NATURALIST. (VoL. XXXV, 
The rhythmical assaults of the Myrmicas on the Leptothorax 
retreat in the afternoon, on several of the days during which 
the ants were observed, is, I believe, to be explained as the 
result of rising temperature. In the Litchfield Hills the nights 
and mornings of late August and early September are rather 
cool, while the noon hours may be very warm. The Lubbock 
nest happened to be placed at a window in a room with south- 
western exposure, so that the diurnal variation in temperature 
must have been keenly perceived by the ants. In the warm 
afternoons the activities of the Myrmicas increased; they ran 
about more rapidly, became more enterprising, and indulged 
their excavating instincts to a greater extent. Then in the 
course of this employment they often broke into the Lepto- 
thorax retreat. 
The fact that the Leptothorax changed their entrances from 
time to time, and, as shown by the figures, kept perfecting the 
form of their cell, thereby making it easier to guard and rebuild | 
and more difficult for the Myrmicas to demolish, is evidence 
of the remarkable psychic plasticity of these ants. Similar 
behavior on the part of ants that have been repeatedly dis- 
turbed by other species are recorded by different observers. 
Forel (94, p. 8) brought a large formicary of Myrmucocystus 
altisquamis from Algiers and gave it an opportunity to establish 
itself in a garden near Zürich. The African ants were much 
annoyed by the incursions of Lasius niger and T: etramorum 
cespitum, and although they at first adhered to their Algerian 
custom of maintaining a large open entrance to their nest, they 
learned during the course of the summer to narrow the oper- 
ing gradually. Finally they plugged it up completely with 
grains of earth and made only a small temporary orifice when- 
ever they strolled out on sunny days. Wasmann (97, pp. 69, 7 9) 
mentions a nest of Formica sanguinea that resorted to a similar 
method of protecting itself from the repeated attacks of a 
neighboring colony of F. pratensis. All these observations 
go to show that Bethe's conception (98;'00) of ants as #7 
“reflex machines” cannot be entertained. 
From the persistent and strenuous efforts of the Leptothorax 
to intrench themselves, and from the shape and character 
