ENGINEERING METHODS 



would be shown correctly by reversing the process of 

 closing gates (Fig. 40), presently to be described. What 

 one first sees is a pair of quivering antennae above one of 

 the pebbles, followed quickly by a brown head, and feet 

 thrust through the interstices of the contingent gravel- 

 stones. 



Then forth issues a single worker, who peeps to this 

 side and that, and after compassing a little circuit round 

 about the gate, or perhaps without further ceremony 

 seizes a pebble, bears it off, deposits it a few inches from 

 the gate, and returns to repeat the task. She is followed, 

 sometimes continuously, sometimes at intervals of ten, 

 twenty, even thirty minutes, by a few other ants, who 

 aid in clearing away the barricade. After that, the 

 general exit occurs. 



On other occasions the method is not so deliberate, or 

 at least it does not appear so. There is a rush of workers 

 almost immediately after the first break, who usually 

 spread over the cone, bustle around the gate, gradually 

 widening the circles, and finally push out into the sur- 

 rounding herbage. At first the exit hole is the size of 

 a pea, and plainly shows that sand and soil have been 

 used under the gravel to seal up the gate. 



The process of closing gates is even more interesting 

 to the observer than the opening, as the various steps 

 are more under his notice. It will best appear by trans- 

 ferring from my notes a few records: About 6 this 

 evening (July 19th) the closing of doors began. At 

 nest A the work was chiefly from within. The workers 

 pushed the sand from the inside outward with their 

 heads. A grass straw about an inch long was brought 

 from the interior and pushed out until it lay across the 

 gate as a stay for the infilling material. Soil was here 



69 



