94 Ohfervatlons on the Hejfiah Fly» 



inkdi which has no dependence upon the wheat in grain, either 

 for food, or as a place in which to depofit any nit or egg for 

 the prefervation of its fpecies ; but is in the winter feafon a 

 chryfalis, and remains through the whole winter in the field, on 

 the green wheat, without fuffering any apparent injury from 

 froft or ihow, and is transformed into a fly, as foon as the' 

 weather becomes warm enough in the fpring. The time when 

 this transformation will begin, appears to depend upon a certain 

 degree of heat in the atmofphere continued for fome length of 

 time, and will therefore vary in the fame climate or part of the 

 country in different years, according as the feafon in the fpring 

 of the year may be more or lefs forward, and will very probably, 

 for the fame reafon, vary much more confiderably in different 

 climates or parts of the country in the fame year ; but although 

 this transformation appears to be effefted by a certain degree 

 of heat, yet it is far from being univerfal in the whole fpecies 

 at the fame time, but continues according to the beft obfcrva- 

 tioris that! have been able to make about three weeks. This 

 variety in the time of making this transformation in the fpring 

 of the year, under the fame circumftances with refpeft to heat, 

 and in the fame feafon, can perhaps be accounted for in no 

 other way than by ftippofrng that it muft proceed from fomething 

 pecuHar in the conftitution of the infcft itfelf ; for it feems not 

 very probable that it fliould be occafioned by the different 

 times in which the infeft may have become a chryfalis in the fall 

 next preceding, after it has been under the fnow, and fubjefted 



