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 disappeare