LARVA.—The young condition or larva of the Lepidopterous Insect is commonly called a caterpillar. It is a somewhat worm-like creature—in old English it was sometimes called {323}palmer-worm—and is composed of a head and thirteen divisions or segments of the body; the first three of the latter are called thoracic, the other ten, abdominal segments; in most caterpillars the terminal two or three abdominal segments are more or less run together, and the ninth may be very small, so that the true number is indistinct. The first three segments bear each, on either side, a short limb, ending in a curved spine; the next two (or three or more) segments are destitute of legs, but on some of the following divisions another kind of leg of a more fleshy character appears, while the body is terminated by a pair of these thick legs of somewhat different form. The front legs are usually called the true legs, the others prolegs, but this latter designation is a most unfortunate one, the term "pro" being in entomology used to signify anterior; it is therefore better to call the three anterior pairs thoracic legs, and the others abdominal feet, distinguishing the hind pair of these latter as claspers. There is, too, an unfortunate discrepancy amongst entomologists in their manner of counting the body-segments, some count the head as the first segment, while others apply this term to the first thoracic segment. The latter is the more correct course, for, as the head is not a single segment it should not be called such in a terminology that affects to be morphologically exact, not simply descriptive. The thoracic legs are transversely jointed (Fig. 165, B), but this is not the case with the abdominal feet, which are usually armed beneath with a circle, or with rows, of little hooks. The thoracic legs are, independent of their form, of a different nature from the abdominal, for these latter disappear subsequently, while the former give rise to the legs of the imago. The number of thoracic legs is always six, except in a few cases where there are none at all; the abdominal feet are much more variable, and exhibit so many distinctions that we cannot here attempt to deal with them. M. Goossens has given a concise and interesting account of this subject,[183] and Speyer[184] a summary of the variety in number and position. The anatomy of the larva is simple in comparison with that of the perfect Insect; its main features will be appreciated from Fig. 165, from which it will be seen that the stomach is enormous, and the silk-vessels are also very extensive.