[184] 
nary nature j the inftances I have already produced 
•will, I flatter myfelf, be thought fuflicient. 
The great variety of fpecies which occur in the 
infeds now under confideration may indeed make an 
enquiry into their particular natures feem not a little 
fntricate and perplexed ; having them, however, Ikil- 
fully reduced under their proper genus, the dif- 
ficulty is by this means confiderably diminifhed. 
All the infeds comprehended under any difliind 
genus, we may reafonably fuppofe to partake of one 
general nature; and, by diligently examining any of 
the particular fpecies, may thence gain fome infight 
into the nature of all the reft. With this view I 
have chofen, ^out of the various forts of Aphides, 
the largeft .of thofe found on the rofe tree; not only 
as its fize makes it the more confpicuous, but as 
there are few others of fo long a duration. This 
fort, appearing early in the fpring, continues late in 
the autumn; while feveral are limited to a much 
■fliorter term, in conformity to the different trees 
and plants from whence they drew their nourifh- 
-ment. 
SECTION I. 
If at the beginning of February the weather hap- 
pens to be fo warm, as to make the buds of the rofe 
tree fwell and appear green ; fmall aphides are fre- 
quently to be found upon them, not larger than the 
young ones in fummer, when firft produced. But 
there being no old ones to be found at this time of 
the year, which in fummer I had oblerved to be 
viviparous ; I was formerly not a little perplexed by 
fuch 
