254 M i c r o s c o p i c a l E s s a y s .
are fome years in a manner freed from them. The fame kind of
animal is then at one time o f the year viviparous, and at another
oviparous.
Thofe aphides which withftand the feverity o f the weather fel-
dom come to their full growth before the month o f April, at
which time they ufually begin to breed, after twice calling off
their exuvia, or outward covering. It appears that they are all
females, which produce each of them a numerous progeny, and
that without having intercourfe with any male infedl; they are
viviparous, and what is equally lingular, the young ones all come
into the world backwards. When they firll come from the
parent, they are enveloped by a thin membrane, having in this
fituation the appearance o f an oval egg; thefe egg-like appearances
adhere by one extremity to the mother, while the young
ones contained in them extend the other, by that means gradually
drawing-the ruptured membrane over the head and body to the
hind feet. During this operation, and for fome time after, the
fore part o f the head adheres,.by means o f fomething glutinous, to
the vent of the parent. Being thus fufpended in the air, it foon
frees itfelf from the membrane in which it was confined; and
after it’s limbs are a little flrengthened, is fet down on fome
tender Ihoots, and left to provide for itfelf.
In the fpring months there appear on the rofe trees but two
generations o f aphides, includmg thofe which proceed immediately
from the laft year’s eggs ; the warmth of the fuminer adds
fo much to their fertility, that no Iefs than five generations
fucceed one another in the interval. One is produced in May,
which calls off it’s covering; while the months o f June and July
each
M i c r o s c o p i c a l E s s a y s . 255
each fupply two more, which caff off their coverings three or four
times, according to the different warmth of the feafon. This frequent
change of their outward coat is the more extraordinary,
becaufe; it is repeated more often when the infefts come the
fooneft to their growth, which fometimes happens in ten days,
where warmth and plenty o f nourilhment confpired.
Early in the month of June, fome of the third generation which
were produced about the middle of May, after calling off their
laft covering, difcover four ereft wings, much longer than their
bodies ; and the fame is obfervable in all the fucceeding generations
which are produced during the fummer months, but Hill
without any diverfity o f fex ; for fome time before the aphides
come to their full growth, it is eafy to diftinguifh which will have
wings, by a remarkable fullnefs of the breaft, which in the others
is hardly to be diftinguilhed from the body. When the laft
covering is rejefted, the wings, which were before folded up in a
very narrow compafs, are gradually extended in a very furprizing
manner, till their dimenfions are at laft very confiderable. '
The increale o f thefe infefts in the fummer time is fo very
oreat, that by wounding and exhaufting the tend-r Ihoots they
would frequently fupprefs all vegetation, had t they not many
enemies to reftrain them. Notwithftanding thefe infefts have a
numerous tribe of enemies, they are hot without friends, if thofe
may be confidered as fuch, who are officious in their attendance
for the good things they expeft to reap thereby. The ant and
the bee are o f this kind, eollefting the honey in which the aphides
abound, but with this difference; that the ants are conllant
vilitors, the bee only when flowers are fearce; the ants will fuck
in