II. Hind wing.—1, 2, subcostal nervules; 3, discoidal nervule; 4-6, median nervules; 7, submedian nervure; 8, precostal nervure; 9, subcostal nervure; 10, median nervure; 11, 12, disco-cellular nervules; a, costal nervure; b, costa or anterior margin; c, apex or anterior angle; d, hind margin; e, tail or caudal appendage; f, anal angle; g, abdominal or inner margin; h, base.
From the sides of the thorax proceed the two pairs of wings, the general structure of which we have already to a certain extent examined. But when we are a little farther advanced in our
insect studies, we shall have to become acquainted with detailed descriptions given as aids to the identification of species. Now, such descriptions cannot be satisfactory, either to the one who gives or to him who receives, unless expressed in such definite terms as render a misunderstanding impossible. A botanist cannot give an accurate and concise description of a flower without the use of certain names and expressions which have gradually become an almost necessary part of his vocabulary; neither can an entomologist give a really useful, and, at the same time, a succinct description of an insect unless he is acquainted with the names of its parts. Therefore, seeing that we distinguish the various species of butterflies and moths mainly by the arrangement and colour of the markings of their wings, it is really necessary that we should know the names of the different parts of these organs. For this reason I have inserted drawings of a fore and of a hind wing of a butterfly, together with the names of the various parts of the wings, and also the names of the principal rays or nervures. Yet I would not advise any young entomologist to attempt to commit to memory all the names given. Rather use the diagram for reference when occasion requires, more particularly when you have an insect in your possession that you desire to study. In ordinary descriptions of butterflies and moths the names of the nervures are not so generally used as those of the parts of the wing. Consequently it is exceedingly useful to know what is meant by the terms base, costal margin, apex, hind margin, anal angle, inner margin, discoidal cell &c. as applied to the wing.
The two pairs of wings are attached to the second and third segments of the thorax; but of the three pairs of legs, which we have next to consider, one pair arises from each of the three segments. The arrangement of these limbs is well shown in the sketch on page 3, as are also the names of the different parts of the limb, the latter being given for reference by the reader when the need arises.
All insects, in their perfect state, we are told, have three pairs of legs; but if you examine the under surface of certain butterflies, such as the Marbled White, or any of the Vanessas, Browns, or Heaths, it is quite likely that you will raise objection to such a statement; for in these you may possibly see only four legs. But this is the result of a too cursory observation. Look a little more closely at your specimen, and you will see a pair of smaller legs folded up under the fore part of the thorax. By means of a blunt needle
you can straighten out these limbs, and then the difference in length to be observed between them and the other four is very striking indeed. They are also thinner than the middle and hind legs; and, unlike these, are not provided with claws.
Fig. 9.—The Undeveloped Fore Leg of a Butterfly.
These imperfectly developed legs are, of course, quite useless as far as walking is concerned; indeed, it is extremely doubtful as to whether they are of any service whatever to the owner. On one