GENERAL ASPECT. 
7 
He says, Leur nombre n’est peut-etre pas inferieur 
a celui des especes des plantes ; car s’il n’est pas sur 
que chaque espece de plante ait son espece particuliere 
de Puceron, il est certain seulement qn’en general des 
plantes de differentes especes ont difierentes especes de 
Puceron, et que souvent plusieurs sortes de Puceron 
aiment la meme plante.’’ 
Neglect of this last observation will partly explain 
the fact, that one species of A]jliis possesses no less than 
thirty synonyms, and again, that the same name 
has been given by authors to six different species of 
Aphis, 
Kaltenbach also says, that observers have been 
deterred from a study of the family from an erroneous 
notion of the multiplicity of its species. Thus Schmid- 
berger recently estimated the number at upwards of 
one thousand, which doubtless is largely in excess. 
The distinctive characters of Aphides are far less 
marked than those of most other insects. Colour, which 
appeals so forcibly to the eye in the Lepidoptera and 
other groups, is here but an insufl&cient guide. The 
young of some species are quite unlike their parents in 
this respect, and their hues vary even in the course of 
a few hours. Again, the adult insects sometimes 
change their prevailing tint, simply through a reduc- 
tion of temperature, at which time they may go through 
all the changing shades of the autumn leaves amongst 
which they nestle. 
When to these difficulties the fact is added, that 
some Aphides show a certain inconstancy of both size 
and colour ; which may be caused by variations in the 
kind of food-plant infested, some indulgence is craved 
if, in the present Monograph, failure hereafter may be 
shown, as to the identification of some British with 
Continental forms. 
The family of Aphides is comprised in the second 
large division Haustellata of the class Insecta. It 
further belongs to the order Hemiptera (Ehynchota of 
Burmeister), which, again, is separated into the sub- 
