Let us begin with the Elephant Hawk-moth.  The caterpillars (Fig. 3), as represented in most entomological works, are of two varieties, most of them brown, but some green.  Both have a white line on the three first segments; two remarkable eye-like spots on the fourth and fifth, and a very faint median line; and are rather more than four inches long.  I will direct your attention specially, for the moment, to three points:—­What do the eye-spots and the faint lateral line mean? and why are some green and some brown, offering thus such a marked contrast to the leaves of the small epilobe on which they feed?  Other questions will suggest themselves later.  I must now call your attention to the fact, that when the caterpillars first quit the egg, and come into the world (Fig. 4), they are quite different in appearance, being, like so many other small caterpillars, bright green, and almost exactly the color of the leaves on which they feed.  That this color is not the necessary or direct consequence of the food, we see from the case of quadrupeds, which, as I need scarcely say, are never green.  It is, however, so obviously a protection to small caterpillars, that this explanation of their green color suggests itself to every one.

[Illustration:  FIG. 5.—­THE CATERPILLAR OF THE ELEPHANT HAWK-MOTH (Chaerocampa elpenor).  Second Stage.]

[Illustration:  FIG. 6.—­THE CATERPILLAR OF THE ELEPHANT HAWK-MOTH (Chaerocampa elpenor).  Just before the second moult.]

[Illustration:  FIG. 7.—­THE CATERPILLAR OF THE ELEPHANT HAWK-MOTH (Chaerocampa elpenor).  Third Stage.]

After five or six days, and when they are about a quarter of an inch in length, they go through their first moult.  In their second stage (Fig. 5), they have two white lines, stretching along the body from the horn to the head; and after a few days (Fig. 6), but not at first, traces of the eye-spots appear on the fourth and fifth segments, shown by a slight wave in the upper line.  After another five or six days, and when about half an inch in length, our caterpillars moult again.  In their third stage (Fig. 7), the commencement of the eye-spots is more marked, while, on the contrary, the lower longitudinal line has disappeared.  After another moult (Fig. 8), the eye-spots are still more distinct, the white gradually becomes surrounded by a black line, while in the next stage (Fig. 9) the centre becomes somewhat violet.  The white lines have almost or entirely disappeared, and in some specimens faint diagonal lines make their appearance.  Some few assume a brownish tint, but not many.  A fourth moult takes place in seven or eight days, and when the caterpillars are about an inch and a half in length.  Now, the difference shows itself still more between the two varieties, some remaining green, while the majority become brown.  The eye-spots are more marked, and the pupil more distinct, the diagonal lines plainer, while the white line is only indicated on the first three, and on the eleventh segment.  The last stage (Fig. 9) has been already described.