BIOLOGICAL PAPERS. 



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closing them a short time before sunset, usually having them closed 

 before darkness comes on. There seems to be only a small force en- 

 gaged in this work. The material used for closing is the same as 

 that used for the covering of the mound. So perfectly are they closed 

 that even close observation does not detect the place. The gates 

 are also closed if a storm is threatening, the force at work being larger 

 and more active. Especially is this true if the storm is fast approach- 

 ing. As soon as the gates are opened the working force is out and 

 soon busily engaged with the work. However, they again return to 

 the formicary for their nooning, not coming out to resume their work 

 until the midday fervor of the sun has passed. If the day is a cool, 

 cloudy one, they do not stop for the noon. It does not follow that 

 the ants are not working because the field-work has ceased at the noon 

 hour. The interior work of the nest certainly requires very much 

 time and labor, and this work is probably in operation during the 

 noon hours, and especially in the morning before the gates are opened. 



NUMBER. DIRECTION AND POSITION OF GATES. 



Beneath the gravelly roofing of the mound is the natural soil, of 

 which the remainder of the mound is composed. The most of this 

 has been brought from below, being the soil removed for the under- 

 ground galleries. This soil is firmly cemented together, forming a 

 hard and almost rain-proof covering. The galleries, into which the 

 gates open, communicate with the galleries, storerooms and living- 

 rooms within the mound and directly beneath the mound. The sub- 

 terranean galleries and chambers are so numerous in many of the 

 mounds that they are simply honeycombed. This is particularly true 

 in that half of the mound next to the external opening, which 

 is illustrated in plates XXVI and XXVIII. The chambers, with 

 their low, arched ceilings and level floors, are of various sizes, be- 

 ing from one to three inches long, and from one-half to one inch 



