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through and through with galleries, most of which lie in hori- 

 zontal strata, but show no such enlargement into chambers at 

 special points as occurs in European hills. The nests when 

 injured are repaired immediately, not by adding grain to grain, 

 to make a solid mass, afterwards to be mined by galleries, but 

 by constructing these galleries at once with little pellets formed 

 of a few cemented grains of earth, fastened to the parts already 

 in place; in this way arches are sprung at needed points, 

 and galleries are formed by filling in the spaces between the 

 arches. Wherever great damage has occurred, the work goes 

 on simultaneously from many centres by the springing of 

 arches from piers erected at symmetrical intervals. In the 

 same way stories are added to the structure. 



The work often goes on with surprising rapidity, so that 

 mounds half the average size of the mature hills may be built 

 in a single year ; but when once they have reached the 

 normal size, a period of thirty years may show little change, 

 the multiplication of the colony being provided for by the 

 construction of new mounds. Mr. McCook estimates that 

 usually nearly thirty cubic decimetres of material are raised 

 by new communities in a single year. As all this has to be 

 brought from beneath the ground, through galleries in direct 

 connection with the interior of the mound, the extent of these 

 underground passages must be very great. By stamping on 

 the ground, one such gallery was traced, just beneath the 

 surface of the soil, for a distance of eighteen metres, and it 

 is probable that there ' are as many subterranean galleries 

 as there are superficial paths. A curious fact was noticed in 

 the orientation of the mounds ; that while they were nearly 

 conical, the longest face of the cone lay toward the west and 

 its steepest slope toward the east ; this peculiarity was only 

 noticed in the mountains and was not invariably true, but ob- 

 tained as a general rule, whatever the slope of the ground. 



Huber states that these ants close the approaches to their 

 nests at night and open them again by day. Forel says that 

 they seem to close them only when they appear to have no 

 further use for them ; and Mr. McCook always found them 

 open. Huber states further that the ants are inactive during 



