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Microscopical Essays, 253 



In order to give a further infight into the nature of thefe infers, 

 I (hall infert an extract of a defcription of the different generations 

 of them by Dr. Richardfon, as publifhed in the Philofophical 

 TranfaelionS) vol. hm 



The great variety of fpecies which occur in the infe&s now 

 under confideration, may make an inquiry into their particular 

 natures feem not a little perplexing,, but by reducing them under 

 their proper genus, the difficulty is considerably diminifhed; We 

 may reafonably fuppofe all the infects, comprehended under any 

 diftin6l genus> to partake of one general nature ; and by diligently 

 examining any particular fpecies,. may thence gain fome infight 

 into- the nature of all the reft. With this view Dn Richardfon 

 chofe out of the various , forts of aphides thelargeft of thofe found; 

 on the rofe tree, not only as it's lize makes it the more con,. 

 fpicuous, but as there are few others of fo long a duration. This 

 fort appears early in; the fpring, andcontinues late in the autumn.; 

 while feveral are limited to a much fhorter term, in conformity, 

 to the different trees and plants from whence they draw, their, 

 nourifhment,. 



1. If at the beginning of February the weather happens to be 

 fo warm as to make the buds of the rofe tree fwelfand appear 

 green; fmall aphides are frequently to be found on them, though; 

 not larger than the young ones in fummer,. when firft produced. 

 It will be found, that thofe aphides wrrieh appear only in fpring, 

 proceed from fmall black oval eggs, which were depoiited on the 

 laft year's moot ; though when it happens that the infecVmake 

 too early an appearance, the greater part fuffer from the fharp 

 weather that ufually fucceeds ; by which means, the rofe trees. 



are 



