1926] Sequential Distribution of Formica exsectoides Forel 135 
The mounds that continued active through 15 years had 
grown variably, from 2 to 12 inches in height and from 5 to 50 
inches in width. Each of the above eight mounds was a foot or 
more in height in 1905 and doubtless of some years’ standing. 
Special attention should be called to the pair of mounds No. 
54 on the edge of a gravel pit which were always conspicuous 
for dark color and coarse sandy surface due to the special en- 
vironment ; there being hereabouts little but subsoil and a growth 
of false indigo which in the fall yielded dark blackish leaves that 
were collected on the nests to such an extent as to make these 
appear very dark. The hills in 1905 were small but not ap- 
parently young; one 9 by 24, the other 4 by 18 inches. In the 
whole 15 years the former grew to be 11 by 29 and the latter 12 
by 36. They had grown almost to touch at the base and one had 
advanced a little over the edge of the cliff. From that period up 
to the present, these two mounds remain but little changed, 
being of very slow growth, apparently resulting from poor con- 
ditions of soil and of vegetation. 
In contrast, the mound No. 59 which was very large in 
1905, being 2 feet by 5 feet, had in fifteen years grown to 32 
inches by 96 inches, measuring 115 inches over its surface and 
with a circumference of 22 feet. This mound in the midst of 
Japanese honeysuckle has always been nearly clear of all but a 
little grass and the vine has stopped rather abruptly at the moat 
or clear area about the base, being restricted in growth by the 
ants of this very successful nest. This mound still continues, 
and though in the past few years it showed signs of weakness in 
lack of growth and poor upkeep it is greatly recovered in 1926. 
Many other cases were recorded showing marked indivi- 
duality in the mounds, not only in architecture and location but 
in longevity, rate and character of growth and decay. 
The individuality of each mound is a result of interaction 
of the environment and the special internal states of each com- 
munity, as failure or success depends upon both external and 
internal factors. 
The mound is not only the abode of the adults but pre- 
eminently the incubator for the young and thus the means of 
securing the perpetuation of the race. The mound is not a tem- 
