338 PROCEEDINGS OF THE ACADEMY OF [1887. 



ing an average depth of eighteen inches. From the points at which 

 the ants came to the surface, the road was continued in a straight 

 line 185 feet further to a tree in a gentleman's private grounds 

 which the ants were engaged in defoliating. The entire length of 

 the roadway was thus 661) feet, and the path as laid out by a young 

 engineer who assisted in the observation, shows scarcely less deflec- 

 tion from a straight course than that of the Rufous ants recorded 

 in the above observation. 



4. Sentinels. The longest of the three trails alluded to made by 

 the Scotch ants terminated upon an oak tree which was also occupied 

 by a colunni of ants from a neighboring hill. The two colunms 

 rigidly maintained their ])laces on opposite sides of the trunk. 

 Sentinels were scattered along either margin of both columns and 

 these exhibited great watchfulness and sensitiveness to the approach 

 of any object. Dr. McCook on approaching his flnger to these 

 sentinels observed that they seemed to perceive his finger when it 

 reached a point an inch or an inch and a half distant from the 

 bark. At once the ants thrust out their antennae, extended their 

 heads, then the two front legs, and finally the middle legs thus 

 hanging to the bark of the tree by the hind legs alone, the abdomen 

 being slightly turned underneath the body as though prepared to 

 eject formic acid upon any adversary. In one case at least the ant 

 hung to the bark by one hind foot alone, extending the whole body 

 in a perpendicular direction from the surface of the tree. It presen- 

 ted a grotesque appearance, and exhibited every sign of eagerness 

 and vigilance in the discharge of its duty as watchman. 



Several individuals were taken from one column and placed in 

 the line of march of the ants from the other nest. They showed the 

 usual evidences of strangeness and failed to fraternize, but on the 

 other hand no one was assaulted by the passers by, a toleration 

 worthy of note as shoAving some degree of community among the 

 various nests of the one species. 



The time which Dr. McCook could give to these observations W'as 

 limited to several hours of a summer afternoon, which he spent as a 

 tourist in this interesting mountain region, but they present some 

 conclusions which a})pear to be reasonably decisive, and which at 

 least may serve to stimulate further observations in the same line 

 extending over greater periods and including a greater number of 

 cases. 



November 8. 

 Mr. Charles Morris, in the chair. 

 Twenty-one persons present. 



