st special
circumstances--such as the number of the slaves as compared with the
number of masters--would tend to develop a greater or less degree of
dependence of the captors or their servitors.

Huber, for instance, informs us that the _Fusca_-slaves of the
_Sanguineas_ of Switzerland work with their masters in building the
nest; they close and open the doors of the hive; but their chief
office appears to be that of hunting for plant-lice. In England, on
the contrary, the slaves are strictly household servants, rarely
venturing out of doors. Such differences depend most probably on the
fact that a greater number of slaves occur in Swiss than in English
nests, and they may therefore be employed in a wider range of duties
on the Continent than at home. A fewer number of slaves, a greater
aptitude on the part of the slaves for their duties, the inability of
the masters to perform the duties of the slaves--each or all of these
causes combined would serve to increase the value of the servitors,
and at the same time to reduce the independence of the masters.

This increase of the value of the slaves as active factors in the ant
community might at length proceed to such extremes as we see
exemplified in the _Polyergus_, already referred to--a race which has
become literally unable to feed itself, and to discharge the simplest
duties of ant existence, and whose actual life is entirely spent in
marauding expeditions on the nests of its neighbors.

The subject of the general intelligence of ants, and of their ability
to adapt themselves to awkward and unusual circumstances, may be
briefly touched upon by way of conclusion.

Between the reason and intelligence of higher animals and the
"instinct" of ants there is unquestionably a great gulf fixed. I make
this statement unhesitatingly, notwithstanding that I should no more
willingly attempt to define "instinct" than to give an exact
definition of "insanity." In the latter case one may make the
definition so limited as practically to exclude all save one class of
cases, or so wide as to include even the judge on the bench. In the
case of instinct, the rigid definition of one authority might cause us
to regard it as the exclusive property of lower forms and as having no
relationship whatever with the mental powers of higher beings; or, on
the other hand, as being but a modified form of, or in some respects
identical with, these very powers. We know too little respecting the
so-