The honey, which was fatal before, is now necessary—­the activity, which before was necessary, is now useless; consequently, with the change of skin, the active, slim larva changes into a white fleshy grub, so organized as to float on the surface of the honey, with the mouth beneath and the breathing-holes above the surface; for insects breathe, not as we do through the mouth, but through a row of holes arranged along the side.  In this state it remains until the honey is consumed; then the animal contracts, and detaches itself from its skin, within which the further transformations take place.  In the next stage the larva has a solid corneous envelope and an oval shape, and, in its color, consistency, and immobility, resembles the chrysalis of a fly.  The time passed in this condition varies much.  When it has elapsed, the animal moults again, again changes its form; after this, it becomes a pupa, without any remarkable peculiarities.  Finally, after these wonderful changes and adventures, in the month of August the perfect beetle makes its appearance.

[Illustration:  FIG. 1.  THE CATERPILLAR OF THE MARBLED WHITE BUTTERFLY (Arge galathea).]

In fact, whenever in any group we find differences in form or color, we shall always find them associated with differences in habit.  Let us take the case of Caterpillars.  The prevailing color of caterpillars is green, like that of leaves.  The value of this to the young insect, the protection it affords, are obvious.  We must all have observed how difficult it is to distinguish small green caterpillars from the leaves on which they feed.  When, however, they become somewhat larger, their form betrays them, and it is important that there should be certain marks to divert the eye from the outlines of the body.  This is effected, and much protection is given, by longitudinal lines (Fig. 1), which accordingly are found on a great many caterpillars.  These lines, both in color and thickness, much resemble some of the lines on leaves (those, for instance, of grasses), and also the streaks of shadow which occur among foliage.  If this be the explanation of them, then they ought to be wanting, as a general rule, in very small caterpillars, and should prevail most among those which feed on or among grasses.

[Illustration:  FIG. 2.—­THE CATERPILLAR OF THE EYED HAWK-MOTH (Smerinthus ocellatus).]

Now, similar lines occur on a great number of caterpillars belonging to most different groups of butterflies and moths, as you may see by turning over the illustrations of any monograph of the group.  They exist among the Hawk-moths—­as, for instance, in the Humming-bird Hawk-moth; they occur in many butterflies, especially in those which feed on grass; and in many moths.  But you will find that the smallest caterpillars rarely possess these white streaks.  As regards the second point, also, the streaks are generally wanting in caterpillars which feed on large-leaved