4 
INTRODUCTION. 
culate in proper arteries and veins ; but is driven from the 
fore part of the heart into the head, and thence escapes into 
the body, where it is mingled with the nutritive juices that 
filter through the sides of the intestines, and the mingled 
fluid penetrates the crevices among the flesh and other in- 
ternal parts, flowing along the sides of the air-pipes, whereby 
it receives from the air that influence which renders it fitted 
to nourish the frame and maintain life. 
Insects are never spontaneously generated from putrid ani- 
mal or vegetable matter, but are produced from eggs. A 
. few, such as some plant-lice, do not lay their eggs, but re- 
tain them within their bodies till the young are ready to 
escape. Others invariably lay their eggs where their young, 
as soon as they are hatched, will find a plentiful supply of 
food immediately within their reach. 
Most insects, in the course of their lives, are subject to 
very great changes of form, attended by equally remarkable 
changes in their habits and propensities. These changes, 
transformations, or metamorphoses , as they are called, might 
cause the same insect, at different ages, to be mistaken for 
as many different animals. For example, a caterpillar, after 
feeding upon leaves till it is fully grown, retires into some 
place of concealment, casts off its caterpillar-skin, and pre- 
sents itself in an entirely different form, one wherein it has 
neither the power of moving about, nor of taking food ; in 
fact, in this its second or chrysalis state, the insect seems to 
be a lifeless oblong oval or conical body, without a distinct 
head, or movable limbs ; after resting awhile, an inward 
struggle begins, the chrysalis-skin bursts open, and from the 
rent issues a butterfly or a moth, whose small and flabby 
wines soon extend and harden, and become fitted to bear 
away the insect in search of the honeyed juice of flowers 
and other liquids that suffice for its nourishment. 
The little fish-like animals that swim about in vessels of 
stagnant water, and devour the living atoms that swarm in 
the same situations, soon come to maturity, cast their skins, 
