11 
forms us, that Reaumur has proved that by some 
species of this genus, in “ five generations, one 
Aphis may he progenitor of 5,900,900,000 descend- 
ants, and it is supposed that in one year there may 
be twenty generations.” He also observes, that at 
the time of emigi’ation, “ these great enemies of 
the world are sometimes so numerous as to darken 
the air.” This is extremely astonishing (yet I 
would not doubt the authenticity of the assertion), 
for although I never saw them so numerous as to 
darken the air, yet I remember seeing, in this 
neighbourhood, in the month of September, I 
believe in the year 1819, the species which infest 
the apple tree alight in clouds, so as almost to 
cover every kind of tree or plant they came in con- 
tact with. It is remarkable, but I believe always ' 
the case, that the apple tree is quite free from j 
this insect from the middle of June to the month 1 
of September, at which time it again becomes ' 
infested with the perfect insect. They then vivipa- 
rously establish their offspring, and this generation, 
in its imperfect state, quits the leaves and deposits 
eggs numerously on the spurs and branches of 
the tree, and then, like all the preceding genera- 
tions, after establishing its progeny, soon dies. 
Nature is wonderfully displayed and the Being of 
an all wise instructor and creator illustriously ex- 
hibited by the instinct of these little animals in 
choosing to establish their ova on the branches and 
not on the leaves, on which they had recently been 
n 2 
