100 Ohfervatiom on the Hejfian Fly, 



not lefs than two months, and may be prolonged to a much 

 longer time by any of tlie caufes before mentioned. AU.thefe 

 feveral caufes of variety in the time of its continuing in this 

 ftate, together with the various times in which it is firft formed 

 into a chryllilis injthe month of June, confpire to render the 

 period of time in which it makes its next transformation into a 

 fly, much longer than any of the other periods of time in which 

 the infeft makes its feveral transformations. It generally 

 begins about the 20th or 25th of Auguft, and continues ina 

 s^reater or lefs degree through the whole month of September, 

 but by far the greater part of the fpecies are without doubt 

 transformed into a fly, in the firft part of 'this latter month. 

 This appears fufficiently evident from this confideration, that 

 wheati fown early enough in the feafon to be up in the firft week 

 in September, will generally be deftroyed ; and on the contraiy 

 when it is fown fo late as not to be up until fome time in 

 Oclober, it will . in great meafure efcape. I have fuppofed 

 this transformation to take place, between the 20th of Auguft 

 and the firft of 08;ober, but this ought no doubt to be under- 

 ftood with fome exceptions ; for it is very probable that in 

 fome few inftances, and in fome particular fituations with re- 

 fpeft to heat and moifture, it may begin fomewhat fooner ; and 

 on the contrary, if the weather fli'ould prove moderate in the 

 month of Oftober, there is no reafon to doubt but that it may 

 continue in fome degree through the greater part of that 

 month. A reflexion will here naturally arife from the fore- 



