5. _Hymenoptera_, membranous winged insects, such as bees, wasps, ichneumon flies, &c. All the four wings are membranous, but they have fewer nervures, and are not reticulated like those of the preceding order. The mouth is furnished with mandibles and maxillæ, and the abdomen is terminated either by an ovipositor or a sting. 6. _Lepidoptera_, or scaly-winged insects. These are the butterflies and moths, which are characterised by the farinaceous or scaly aspect of their wings, and the tubular or thread-like extension of the parts of the mouth. 7. _Strepsiptera_ or _Rhipiptera_, with twisted wings. These creatures resemble the ichneumon, in laying their eggs in the bodies of 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. _Suctoria_, 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 woodwork, 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. _Myriapoda._ This order is made a separate class by many naturalists, 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 principal insects in this order are included in the Linnæan 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, however, 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 Myriapoda, which are also without wings, do not undergo any metamorphosis. THE RADIATED ANIMALS