No. 418.] NESTS OF AMERICAN ANTS. 795 
Gedanken," which he puts in the form of the following ques- 
tion: “If natural selection can bring about such a peculiar 
development of the instincts in the dominant species, why has 
it not exercised a corresponding influence over the enslaved 
species?" Wasmann is evidently bent on rescuing that por- 
tion of the argument not expressly stated by McCook, viz., 
the necessity of a change of character in the ants of the 
colonies attacked by Polyergus. But closer inspection shows 
this attempt to be unsuccessful, for he has not considered the 
question of the relative abundance of the dominant and aux- 
iliary species. That this is a matter of some moment in a 
discussion of this kind is seen from a general survey of para- 
sitic and predaceous organisms. These must of necessity live 
on that margin of surplus vitality and reproductivity so char- 
acteristic of all animals and plants; for it is obvious that 
organisms which depend very decidedly for their sustenance 
on special hosts or prey must endanger their own existence 
to the extent that they endanger the existence of the species 
on which they depend. The serious injury or death of the 
host species implies the death of the parasitic species in all 
cases where the relations between the two are of a highly 
specialized character. This argument could be adduced if the 
Polyergus were more abundant or quite as abundant as the 
auxiliary species. But it is quite unnecessary to make use of 
it, because Polyergus is a rare ant of local occurrence, and the 
various forms of F. fusca and F. pallide-fulva which it enslaves 
are widely distributed and vastly more abundant both in col- 
onies and individuals. In fact, no other insects are as com- 
mon in our Northern States as the varieties of these two ants, 
and even in Texas, near the southernmost limits of the dis- 
tribution of F. fusca, a form very closely related to F. sub- 
sericea, viz., F. gnava Buckley, is the most prolific of ants. Its 
nests often contain upwards of thirty fertile queens, and the 
number of eggs, larvae, and pupa which are reared between 
the end of February and the first of June is enormous. Why, 
then, should these very prolific and widely distributed species 
exhibit a special development of valor or a particular defensive 
form of nest architecture in adaptation to a rare predaceous 
