1878. | Mound-Making Ants of the Alleghenies. . 439 
in erecting an adult hill, from 3 to 7 years, is compared with 
the thirty years which one hundred thousand men spent in build- 
ing the pyramid. Moreover, as will also appear, the superstruc- 
ture or hill, is by no means the whole of the formicary. A vast 
system of subterraneous galleries penetrates the earth to unknown 
depths and distances, requiring labors which in magnitude may 
well be compared with those which excavated the catacombs of 
Rome. 
Sentinels—I observed on the tree-paths a movement that had the 
appearance of some policy of police. Workers, with the normal 
round black abdomen, were scattered at intervals along the trunk. 
They did not seem to belong to the line of ascending foragers, 
but rather to be stationary, as though they were sentinels or 
policemen. They were active in challenging with their antennz 
the repletes who were on the return, and were quick to resent any 
interference made by intruding a finger or straw upon the path. 
This statement is made with reservation, as I was not able fully to 
Satisfy myself that the facts revealed a fixed habit. The point, 
owever, is well worthy of future investigation. There is at least 
a probability, from analagous habits of the ant, that the individ- 
uals referred to above were indeed sentinels as their behaviour in- 
dicated. It is a well established fact, in the economy of ant hills, 
that’ sentinels are posted at or near entrances, and common ave- 
nues of approach. I satisfied myself of this by very many observa- 
tions and experiments, which it is not necessary to relate in detail. 
It will suffice to say that on every occasion of approach of any 
object to a hill or entrance, workers instantly sprang upon the 
surface. These sentries were constantly seen lurking just inside 
the gallery doors, whence they issued with every mark of intense 
vigilance and excitement the moment a finger was intruded or the 
Smallest object dropped near them. Frequently they patrolled the 
Vicinity of the gates. They attacked every intruder with the ut- 
Most promptness and intrepidity. It gave subject for great won- 
der to note the rapidity with which an alarm was communicated — 
throughout a large hill. Two hills in particular, whose inhabi- 
tants were for several days in a condition of high nervous excite- 
ment, attracted attention. Standing a yard or more from the base, 
I would agitate with my foot a stone which evidently had com- 
munication with the interior of the mound. There was scarcely 
an appreciable interval of time ere the whole surface of the cone- 
