We have already referred (page 28) to caterpillars that walk by a series of strides, alternately looping and extending their long and slender bodies. It is this peculiar characteristic of the larvae of the present division that suggested the name _Geometrae_--a term that signifies 'earth-measurers,' for they appear to measure the ground over which they travel in terms of their own length. We have also dealt with the peculiarities of structure in the case of these caterpillars--peculiarities which adapt them to this mode of progression; and we have now to make a selection from the various families of this important division for a more detailed description. The _Geometrae_ include nearly three hundred species and sixteen families. The moths have slender bodies and full wings, and generally rest with the latter outspread. A few, however, repose with wings erect like the butterflies, and a small number conceal their hind wings after the manner of the _Noctuae_. Family--UROPTERYGIDAE _The Swallow Tail_ (_Uropteryx sambucaria_) Our first family--_Uropterygidae_--has only one British representative, and that is the well-known Swallow Tail, so common in gardens and among hedgerows in the south of England. This species is shown on Plate XII (fig. 2), and the insect is so readily identified by the conspicuous 'tails' on the hind wings that no written description will be necessary. The caterpillar is a most peculiar and interesting creature. Its colour is very variable, being either brown, olive, ochreous, or reddish; and it is notched or humped in such a manner that it exactly resembles a twig. This strange imitation is rendered still more remarkable by the attitude assumed by the caterpillar when at rest. It fixes itself to a twig by means of its two pairs of claspers, with its body standing out at an angle in a perfectly straight posture; but its head is always supported by means of a very slender and almost invisible silk fibre. It feeds on a number of plants and trees, including elder (_Sambucus nigra_), blackthorn (_Prunus spinosa_), whitethorn (_Crataegus oxyacantha_), bramble (_Rubus fruticosus_), honeysuckle (_Lonicera Periclymenum_), and forget-me-not (_Myosotis arvensis_). It may be found feeding in the autumn, or hybernating in the crevices of the bark of trees in winter. In April or May it comes out again; and in June, in which month it is full grown, it binds together some fragments of leaves, and forms them into a little swinging hammock in which it changes to a brown chrysalis spotted with black. Just at this time it seems to be particularly sensitive. In the caterpillar state it will strongly resent any kind of disturbance, and will give a blow to an intruder by suddenly swaying its body right and left; and while in its hammock a gentle irritation, such as a puff of wind from the mouth, will set it wriggling in a furious manner. Family--ENNOMIDAE