﻿March i89S-] LaNDER. DoMES OF CiCADA SK.PTENUECIM -35 



side, and the radiation carried off by the breeze, prevented an 

 early revival of the unsheltered pupte ; which at their proper season 

 emerged from open shafts. 



A somewhat similar case is where domed burrows were obser- 

 ved near Washington at a former advent, in a thick pine grove. 

 Here, the protection from the wind by the deep, overhanging cur- 

 tains of the evergreens, would prevent, in a measure, a too rapid 

 waste of the diffused warmth ; while the constant radiation by 

 night of absorbed heat stored up by day among the thick foliage 

 would tend to offset the loss from the ground ; rendering the tem- 

 perature like that in the cellar, practically the same, day and 

 night ; doubtless raising it enough ovv^r that in the exposed places 

 outside (where the wind would act as a fan,) to supply sufficient 

 warmth to revive the pupae : it may be only a week or two before 

 those not thus protected. This, of course, is assuming that the 

 domed burrows were shallow — the pupa^ nearer the surface than 

 those outside, which might have been the case for one or more of 

 several reasons : the insects might not have burrowed much or 

 any below their root-supplies, from which they obtain subsistance, 

 or from other causes which will be referred to later. 



If this theory of unusual warmth and shallow burrows is to 

 hold, the temperature at the time the millions of domes were built 

 on the Nyack hills and the Palisades must have been far above 

 normal, and the localities must have had features that would pre- 

 vent deep burrowing It is susceptible of proof that these con- 

 ditions existed. March of 1894 was unusually warm : the hottest 

 March on the records of the New York weather Station, extending 

 to 1870, and was 223 degrees in excess of normal. At Nyack it 

 was even warmer, as shown by published records. Wild flowers 

 blossomed a month ahead of their season. Even as far up as 

 Poughkeepsie, where domed burrows were found, the recorded 

 temperature was practically the same as at New York. A large 

 part of the dome areas had been burnt over early in March. In 

 these places the combined natural and accidental heat no doubt 

 brought the pup^e speedily to the surface. Even where the leaves 

 and underbrush had been burnt off the preceding Fall the heat 

 of the sun would sooner penetrate the bare ground. 



The Nyack hills and the Palisades are composed of massive 

 rock ; their summits ground off by glacial action. These heights 

 are thinly covered with earth ; the extreme elevations, more or 



