ENGINEERING METHODS 



by their relative importance in the military methods of 

 the period. It has now wellnigh ceased, except as a 

 quaint survival of mediaeval ways in castle and town, 

 or as a relic of military days and discipline. It is in- 

 teresting to find among the communal habits of some 

 species of ants a like marked attention to opening and 

 closing the public gates. And this is not a mere survival 



Fig. 39 OCCIDENT ANTS : SINGLE AND DOUBLE GATES OPEN 



of a habit out of which the soul has gone, but is kept up 

 seriously as an important part of the communal de- 

 fences. Though the writer confesses that more than 

 once he has found himself questioning its utility; which 

 probably means his inability to perceive the same. 



Among the communities most persistent in keeping up 

 this habit are those of the Occident ants, and examples 

 of the custom as it obtains among them, and in one 

 other species, will sufficiently illustrate the author's 

 observations. In form the gates of Occidentalis are 

 funnel-shaped openings through the gravel roof of the 

 central mound into the interior, at an inclination of 

 about forty-five degrees. There is usually but one gate, 

 located about one-third of the way from the base. It 

 is single or double, according as it opens into one gallery 

 or two, the former being about three-fourths of an inch 

 wide, the latter from one and a half to three inches (Fig. 



39) . Within, the terminating galleries are quite smooth; 



67 



