﻿34 Journal New York Ent Soc. [Vol. hi. 



an attempt at an explanation of the mystery ; a criticism of my 

 theory appeared in the issue of Nov. loth, and my reply in that of 

 Nov. 27th ; to all of which the reader is referred. 



Hitherto it has been supposed that the object of these domed 

 extensions was to protect the burrows from overflow of water, and 

 that when found on high ground they had been built by pups 

 that had inherited the instinct from ancestors that had lived in 

 "low, wet places". But this theory has been completely over- 

 thrown by the fact that millions of domed burrows were found on 

 the summits of lofty elevations, not "subject to overflow", at 

 Nyack, and many other places visited, and none of the vast army 

 of builders chose "low, wet places"; notwithstanding that the 

 lower levels swarmed with the insects, the ground in many places 

 having been honey-combed with their open burrows. One salient 

 fact is worth a volume of generalizations ; but further proof that 

 the theory is untenable will be offered hereinafter. 



The explanation I have advanced as to the cause of the inter- 

 esting phenomonon is based on the fact that in order to be revived 

 so much in advance of pupte which later emerged from open 

 burrows, the dome-builders must have been near enough to the 

 surface to feel the vivifying effects of abnormal, unseasonable 

 warmth. Of course it must be remembered that our sensation of 

 warmth as to degree and that of the insects are two entirely different 

 things. 



In the Rahway case the features of abnormally high temper- 

 ture (compared to that outside,) and shallow burrows are self- 

 evident. The excavation had reduced the depth of the pupae from 

 the surface. The heat of the sun on the exterior of the enclosure 

 would reach the chamber by conduction and be stored up; making 

 the temperature practically the same night and day, since the 

 warmth could not be carried off by radiation. Thus we often see 

 vegetables sprouting in cellars in the depth of a cold winter. It 

 is altogether logical to suppose that sufficient warmth would obtain 

 to reach the pupae in their artificially shortened burrows and revive 

 them. Having opened their shafts while undeveloped their reason 

 impelled them to close the orifices, perhaps in an attempt to lessen 

 the too rapidly developing warmth, and as a protection against 

 mice and other vermin. The tubular form of the roof showing 

 the "persistance of habit"; their seventeen-year underground 

 work having been of that nature. The normal temperature out- 



