AN ENCYCLOPADIA 
OF HORTICULTURE. 183 
Insects—continued. 
of the others, which, despite this aid, are often but 
too wide-spread and serious. 
Space will not here permit of more than a very brief 
sketch of some of the leading points in the structure 
and life-history of the class and of its leading orders, 
with a mere indication, in the most general terms, of 
the more conspicuous damage done by them, and of the 
means of remedy generally applicable; but fuller infor- 
mation will be found plentifully scattered through this 
work under the various headings referred to below. 
The word “Insect” literally means any 
animal which has the body so divided as 
to seem cut into successive parts, usually 
resembling rings of hard substance, con- 
nected by soft skin. The name has been 
used to include all the animals with bodies 
resembling a row of joints, even Worms 
having been at one time included among 
Insects, along with Spiders, Mites, Crabs, 
Woodlice, and Centipedes. At the present 
time, the name is confined to a considerably 
smaller group of animals—the true Insects 
—though some authorities still include with 
these the other groups named above, except 
Worms. In this restricted sense, the class 
of Insects is composed of animals that 
possess a jointed body made up of a num- 
ber (twenty or twenty-one) of rings of 
horny substance (chitine), connected by skin, so united 
as to form three great divisions in the body, viz., the 
head, the thorax, and the abdomen; that have antenne, 
or feelers, on the head, and three pairs of horny jointed 
legs, and usually two pairs of wings, on the thorax; 
that breathe by tubes (trachew) all through the body 
and limbs, which tubes open on the surface of the body 
by small holes (spiracles); and that, in course of growth, 
pass through a succession of changes (metamorphoses), 
beginning with the egg, and going on through the stages 
of larva and pupa (chrysalis), before assuming the per- 
fect condition (imago), in which alone they present 
all the characters enumerated above. This series of 
changes may be of two kinds. In one, the larva, on 
emerging from the egg, resembles the mature Insect in 
form, and differs from it only in size, and in the entire 
absence of wings; while the pupa differs from the mature 
Insect only in the wings, though indicated, being small and 
rudimentary. Both larva (see Fig. 314) and pupa are 
also sexually immature. This kind of metamorphosis is 
said to be incomplete. Complete metamorphosis differs 
Fig. 289, LARVA OF SMALL CABBAGE BUTTERFLY, 
’ rn > ee t et. 8 
Fig. 290. LARVA OF LEOPARD MOTH. 
from this in the larva (see Figs. 289, 290, and 291) being 
_ quite unlike the mature Insect. Very generally, it re- 
sembles a worm in its form. It may have a distinct 
head, and the rings of the body, though like one another, 
may differ in the three immediately behind the head 
each bearing a pair of horny jointed legs, while those 
of the hinder part of the body may bear skinny suckers 
(prolegs) — the number varies considerably, and they 
may be quite absent. Larvæ of this type (see Fig. 291) 
are called Caterpillars, and are met with among the 
Butterflies, Moths* and Sawflies. Another group of In- 
Sects, in the larval state, are footless creatures, frequently 
Insects—continued. - 
scarcely showing even a trace of a head. Such larvae 
are familiar to everyone under the name of maggots or 
grubs, e.g. those of Bees, Flies, &c. (see Fig. 311). The 
pupe of Insects that undergo a complete metamorphosis 
are not able to move about or to feed, but remain 
helpless for a longer or shorter period, while changes 
are going on within, which result in the development of 
the perfect insect (imago), showing all the distinctive 
characters already set forth. These quiescent pupæ 
differ much from the larve (see Fig. 309), as they show the 
Fig, 291. LARVÆ OF ROSE-LEAF SAWFLY, 
future limbs (antennw, legs, and wings) of the imago, 
though these parts are still useless, and of very small 
size. The Butterflies and Moths, while pupw, have the 
whole body enveloped in a hard crust, which binds down 
all the parts immovably to the body, leaving only a 
slight power of movement in the hinder rings. When 
the pupa is helpless, its safety is generally provided 
for by the larva forming a cell or cocoon of silk, | 
earth, or other material, compacted with a cement from 
its mouth, in which the pupa lies concealed till the 
imago breaks out from it, and crawls to the outer air, 
with wings at first crumpled and useless, but soon ex- 
panding and becoming firm to carry it in flight through — 
the air. Whatever the degree or kind of metamorphosis _ 
undergone by it, the Insect, in its progress from the egg 
to maturity, grows frequently with enormous rapidity. 
The outer coat of the body is too rigid to allow of the 
corresponding extension in it; but the difficulty is met 
by the larva several times (four times or oftener) throw- 
ing off its skin. The old skin separates from the body of _ 
the larva, it splits along the back in front, and the larva 
wriggles its way out, frequently with a skin of a very 
different colour from that in which it had previously 
shown itself. In like manner, the skin of the pupa 
bursts to set free the imagos © 
iden and mysterious appearance of certain 
— oom time led to the belief that they 
—— their life-histories has proved conclu- 
sively that they always originate from parents, though 
at times, in the case of certain Insects, ¢.g., several of 
the true Gall-flies of the Oak-tree, the parents and the 
immediate offspring may differ considerably in appear- eh 
The females produce eggs, except in a few groups, _ 
—— a Aphides, in which the young Insects may b 
brought forth, not sexually by eggs, but by & process — 
of budding. In the case of a few other Insects, the 
s are hatched while still within the body of the 
mother, which thus gives birth to living young or larve. 
The fact that Insects are always p: from parents, 
renders it of the utmost importance, when dealing with 
the injurious species, to become familiar with the habits 
of the females as well as of the larye, which latter are 
usually the destructive agents, and are therefore the more 
