368 CLAUDE FULLER. 



nearly to the crust of the mound, and at times small tubes 

 are driven from them, into the crust. What the purpose of 

 the mound is, is one question ; what it is, is another. The 

 mounds do not begin in a small way and gradually increase 

 in size. No amount of field observation can discover the 

 mounds of T. natal en sis in stages of growth below a certain 

 minimum size,' and there is every reason to believe that a 

 mound of some magnitude is built up suddenly. This may 

 synchronise with that moment when the colony has attained 

 a certain strength, and an extensive addition to its domicile 

 is called for. Even the minimum mound (a primary) contains 

 more nniterial than is represented by the nest-cavity below it. 

 The material used for the building of a mound is, no doubt, 

 obtained b}' increasing the diameter of existing galleries and 

 extending them. Whatever it may be that leads to the 

 formation of a fairly large primary mound, the subsequent 

 growth of the mound is due to the fact that it is the dump 

 for the soil removed in driving galleries through the soil ; 

 and the bulk of the soil in a mound, of almost any magnitude, 

 is the material removed in mining far-reaching stopes. 'J'he 

 purpose of the mound is primarily for the protection of the 

 nest from subsidence. From the position of the queen-cell it 

 is obvious that the extensions of the cavity are for the 

 greater part around and above it. This is evidenced by the 

 fact that in the high mounds the upper region of the cavity 

 is above normal soil level (PI. XXYIII, fig. 2). The ordinary 

 mound, therefore, serves a double purpose, protecting the 

 cavity from subsidence and submersion on the one hand, and 

 jDcrmitting its upward extension on the other. Also the great 

 shafts which perforate the mound are utilitarian, permitting a 

 multitude of miners to reach the crust rapidly and super- 

 impose an extra layer of cement whenever occasion demands. 

 At the same time, they aid in aerating the whole nest-system. 



' The smallest nest I kuow of was found by Dr. Warren. This. I am 

 informed, had a diameter of about 18 in. and a height of about 

 15 in. The nest-cavity was considerably smaller than the mound. 

 The (jueen-cell was found, l)ut the nest was entirely deserted. 



