ENGINEERING METHODS 



as well laid out as are works of a corresponding nature 

 done by the engineering skill of men. And these are 

 not isolated cases, but mark the general rule. The 

 mound-making ants (Formica exsectoides) of America, 

 which so closely resemble Formica rufa in their archi- 

 tecture and general habits, show like characteristics in 

 their road-making, though I do not remember to have 

 seen it displayed under such difficulties. 



The question inevitably arises, How did the ants 

 manage to lay out these roads with such precision? 

 When a corps of engineers or road-builders produce like 

 results, we easily call up certain steps that have been 

 taken. We think of two or more persons, provided with 

 surveying instruments, all dominated by the sense of 

 sight, and controlled by reasoning upon the facts and 

 figures entering into the problem, making out certain 

 lines, and, as far as conditions allow, laying out the 

 course in a straight line between the points to be 

 connected. 



In the case of the ants we start under the embarrass- 

 ment of not having the facts to reason from. Were 

 the roads marked out at once, or are they a gradual 

 growth? We do not know. Has the direct course been 

 determined by a great number of experiences, of which 

 the errors in direction were gradually eliminated, and 

 the final result viz., the shortest path to the desired 

 point retained? We do not know. 



It is easy enough to understand how, after a course 

 has once been fixed, the ants follow it unhesitatingly. 

 Their antennae, which are continually waved before them 

 and to every side, at once detect the strong odor of 

 formic acid on the trail. This is a perfectly accurate 



guide, and beyond doubt it is thus that the workers pass 



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