xx Introduction. 
7. Strepsiptera or Bhipiptera, with twisted wings. These creatures re- 
semble the ichneumon, in laying their eggs in the bodies oi 
other insects, though they generally attack wasps and bees. 
The principal genera are Xenos and Stylops. They are generally 
considered to be closely allied to the Beetles. 
8. Diptera, or two-winged insects, including the flies. The mouth 
is furnished with a proboscis, and there are two small wings 
called halteres placed behind the true wings, which act as 
balancers. 
9. Sucioria, or sucking insects, such as the flea, which have no wings, 
but are furnished with an apparatus for sucking blood. 
Section II. Insects not undergoing Metamorphosis. 
10. Thysanoura, or spring-tail insects. These creatures are of small 
size, and without wings ; they are found in crevices of wood- 
work, or under stones. The principal genera are Lepisma and 
Podura. 
11. Parasita, or parasitical insects, such as the louse. They are also 
without wings. 
12. Mi/riapoda. This order is made a separate class by many natural- 
ists, as the creatures contained in it are distinguished from the 
true insects by the great number of their feet ; by the want of 
distinct divisions into thorax and abdomen ; and by the great 
number of segments into which the body is divided. The prin- 
cipal insects in this order are included in the Linnaean genera 
Julus and Scolopendra, commonly called centipedes. 
The term larva is applied to the young of all insects, included in the 
first nine orders, when first hatched. The different kinds have, how- 
ever, other names ; that is to say, the larva of a butterfly, or moth, is 
called a caterpillar; that of a beetle, a grub; and that of a fly, a 
maggot. The larva changes its skin several times, and at last goes 
into the pupa state, when it is called a chrysalis, an aurelia, or a 
nymph. Sometimes the pupa is wrapped up in a loose outer covering 
called a cocoon. From the pupa in time bursts forth the imago, or 
perfect insect. The Apterous, or wingless true insects, and the Myria- 
poda, which are also without wings, do not undergo any metamor- 
phosis. 
THE KADIATED ANIMALS 
Are so called because their organs of locomotion, and even their inter- 
nal viscera, are generally arranged in a circle round a centre, so as to 
give a radiated appearance to the whole body. The animals included 
in this class are the very lowest in the scale ; they have scarcely any 
external senses ; their movements are slow, and almost their only sign 
of life is a craving for food. Some of them, however, have a distinct 
mouth and alimentary canal, with an anal orifice ; others have a bag- 
like stomach with a kind of mouth, through which they both take their 
food and reject their excrements ; while others have no mouth, and 
appear only to absorb nourishment through pores. In the like manner, 
though some are oviparous, others may be propagated by division into 
plants. Of these Cuvier makes five classes : 
