. Bulletin - United States National Museum. Science. BULLETIN 67, UNITED STATES NATIONAL MUSEUM. legs, and the mesothorax and metathorax ordinarily have each a pair of wings. Behind the thorax is the abdomen, bearing at its tip the genitalia, sting, ovipositor, or sometimes jointed setae or cerci. Insects are bisexual, there being a male and a female form. In some social insects there are other forms known as workers and sol- diers. The female commonly deposits eggs, but in some cases living larvae. The eggs hatch into larvae; the larvae feed, molt, or change their skin several times, and then
. Bulletin - United States National Museum. Science. BULLETIN 67, UNITED STATES NATIONAL MUSEUM. legs, and the mesothorax and metathorax ordinarily have each a pair of wings. Behind the thorax is the abdomen, bearing at its tip the genitalia, sting, ovipositor, or sometimes jointed setae or cerci. Insects are bisexual, there being a male and a female form. In some social insects there are other forms known as workers and sol- diers. The female commonly deposits eggs, but in some cases living larvae. The eggs hatch into larvae; the larvae feed, molt, or change their skin several times, and then turn into nymphs or into pupae. The nymph is active and feeds in a similar manner to the larva, but shows small wing-pads on each side of the thorax, the rudiments of the future wings. From the nymph there issues in time the winged insect. This development through the nymphal stage is called an incomplete metamorphosis. Most insects, however, change from the larva to the pupa, which is quiescent and does not feed, and dif- fers greatly from the larva in appearance (fig. 2). This pupa may be naked, as a chrysalis, or inclosed within a cocoon of silk or earth. From the pupa there issues in due time the winged insect. This line of m? fr development is called Fig. 2.—Diabrotica 12-punctata, showing transformations: a, complete meiamor- beetle; b, egg; c, larva; d, end of larva; e, work of larva; phosis. These differ- ences above noted are not only external. In the case of a complete metamorphosis, the changes that occur inside of the pupa are often revolutionary in the extreme. The entire internal structure, except the nervous system, may be reduced to a mass of liquid, and the organs of the mature insect developed from this liquid. The wings of the anterior pair in insects are called the forewings or primaries, and the others the hind pair, or secondaries. When the forewings are thickened, they are called tegmina or elytra. The wings have numerous veins through them, the arrang
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