rious
resemblance to spotted snakes.

[Illustration: FIG. 10.--THE CATERPILLAR OF THE SMALL ELEPHANT
HAWK-MOTH (_Chaerocampa porcellus_).]

Moreover, we may learn another very interesting lesson from these
caterpillars. They leave the egg, as we have seen, a plain green, like
so many other caterpillars, and gradually acquire a succession of
markings, the utility of which I have just attempted to explain. The
young larva, in fact, represents an old form, and the species, in the
lapse of ages, has gone through the stage which each individual now
passes through in a few weeks. Thus, the caterpillar of _Chaerocampa
porcellus_, a species very nearly allied to the Elephant Hawk-moth,
passes through almost exactly the same stages as that species. But it
leaves the egg with a subdorsal line, which the caterpillar of the
Elephant Hawk-moth does not acquire until after its first moult. No
one can doubt, however, that there was a time when the new-born
caterpillars of the small Elephant Hawk-moth were plain green, like
those of the large one. Again, if we compare the mature caterpillars
of this group of Hawk-moths, we shall find there are some forms which
never develop eye-spots, but which, even when full grown, correspond
to the second stage of the Elephant Hawk-moth. Here, then, we seem to
have species still in the stage which the Elephant Hawk-moth must have
passed through long ago.

The genus _Deilephila_, of which we have three species--the Euphorbia
Hawk-moth, the Galium Hawk-moth, and the Rayed Hawk-moth--is also very
instructive. The caterpillar of the Euphorbia Hawk-moth begins life of
a clear green color, without a trace of the subsequent markings. After
the first moult, however, it has a number of black patches, a white
line, and a series of white dots, and has, therefore, at one bound,
acquired characters which in the Elephant Hawk-moth, as we have seen,
were only very gradually assumed. In the third stage, the line has
disappeared, leaving the white spots. In the fourth, the caterpillars
have become very variable, but are generally much darker than before,
and have a number of white dots under the spots. In the fifth stage,
there is a second row of white spots under the first. The caterpillars
not being good to eat, there is, as has been already pointed out, no
need for, or attempt at, concealment. Now if we compare the mature
caterpillars of other species of the genus, we shall find that they
represent phases in