Some captured females laid single eggs sparsely on grass, wood,
and especially on the tarlatan with which the breeding-cage was
covered. The eggs are nearly spherical, but somewhat compressed, of a
grass-green colour, a little lighter, and somewhat larger (1.2 millim.)
than those of _Deilephila Euphorbiæ_. During the development of the
embryo the eggs first became yellowish-green, and finally yellowish.
_First Stage._
The young caterpillars are four millimeters in length, and immediately
after hatching are not green, but of a yellowish-white opalescent
colour, the large and somewhat curved caudal horn being black. The
caterpillars were so transparent that under a low magnifying power the
nervous, tracheal, and alimentary systems could be beautifully seen.
As soon as the larvæ began to feed (on _Epilobium parviflorum_) they
became green in consequence of the food appearing through the skin, but
the latter also gradually acquired a dark green colour (Pl. IV., Fig.
17). All the specimens (some twenty in number) were exactly alike, and
showed _no trace of marking_.
_Second Stage._
The first ecdysis occurred after 5-6 days, the length of the
caterpillars being from nine to ten millimeters. After this first moult
they appeared of a shining green, the horn, which was black during the
first stage, becoming a little red at the base, while a fine white
subdorsal line extended from the horn to the head (Fig. 18). The head
and legs were green; the divisions between the segments appeared as
fine light rings, and the entire upper surface of the segments was also
crossed by fine transverse rings, as was also the case in the first
stage.
At the beginning of the present stage no trace of the eye-spots could
be detected; but a few days after the first moult it was observed that
the white subdorsal line was no longer straight on the fourth and fifth
segments, but had become curved upwards into two small crescents. The
latter soon stood out more strongly, owing to the filling up of their
concavities with darker green. These are the first rudiments of the
eye-spots (Figs. 19 and 30). A very fine white line now connected the
spiracles (infra-spiracular line), and could be traced from the last
segment to the head. This line takes no further part in the subsequent
development of the markings, but disappears in the following stage. The
blood-red colour of the base of the black caudal horn is retained till
the fifth stage, and then also disappears.
Before the second moult, which occurs after another period of 5-6
days, the caterpillars, which were about 1.3 centimeters in length,
had assumed their characteristic tapering, slug-like form. I did not
notice that the larvæ at this stage possessed the power of withdrawing
the three foremost segments into the two succeeding ones, as is so
frequently to be observed in the adults; neither were these two
segments so strikingly enlarged as they are at an earlier period.
_Third Stage._
After the second ecdysis the marking and colouring only undergo change
with respect to the eye-spots. The concavities of the crescent-shaped
portions of the subdorsal line become black,[70] the remainder of this
line at the same time losing much of its whiteness, and thus becoming
less distinct, whilst the crescents assume the appearance of small
eye-spots (Fig. 20). During this stage the curved, crescent-formed
portions become prepared for complete separation from the remainder
of the subdorsal line; and just before the third moult the eye-spots
become sharply defined both in front and behind, whilst the black
ground-colour curves upwards, and the white spots gradually become
lenticular and commence to enlarge (Fig. 21).
_Fourth Stage._
The third moult takes place after another interval of 5-6 days, the
eye-spots then becoming very prominent. The white nucleus of the front
spot is kidney-shaped, and that of the hind spot egg-shaped; whilst
the black ground-colour extends as a slender border upwards along the
sides of the spots, but does not completely surround them till towards
the end of the present stage (Fig. 21). The central portion of the
white spots at the same time becomes of a peculiar violet-brown colour
inclining to yellow above, the peripheral region alone remaining pure
white.
Of the subdorsal line only traces are now to be recognized, and these
are retained, with almost unchanged intensity, sometimes into the last
stage, remaining with the greatest persistence on the three front and
on the penultimate segments, whilst on those containing the eye-spots,
_i.e._, the fourth and fifth, not a trace remains. At the present stage
the peculiar mingling of colours becomes apparent over the whole of
the upper surface; the green is no longer uniform, but a mixture of
short and gently sinuous, dark green striations on a lighter ground
now appear. On the sides of the caterpillar these stripes, which are
at first indistinct, but become more strongly pronounced in the next
stage, are arranged obliquely on the spiracles, with the lower portions
directed forwards.
_Fifth Stage._
The fourth moult occurs 7-8 days after the third, the caterpillar being
4-5 centimeters in length. Whilst all the specimens hitherto observed
were with one exception light green, they now mostly changed their
colour and became dark brown. In one case only did the brown colour
appear in the previous (fourth) stage. The striations previously
mentioned appear as dull and interrupted dirty yellow streaks, the same
dirty yellow colour showing itself continuously on the sides of the
four front segments. Of the subdorsal line only a distinct trace is
now to be seen on the eleventh and on the three front segments, whilst
on the third segment the formation of another eye-spot commences to
be plainly perceptible by a local deposition of black (Fig. 23). This
third spot does not, however, become completely developed, either in
this or in the last stage, but the subdorsal line remains continuous
on the three front segments. Among other changes at this stage, there
occurs a considerable shortening of the caudal horn, which at the same
time loses its beautiful black and red colours and becomes brownish.
The two large eye-spots have now nearly attained complete development.
The kidney-shaped white spot has become entirely surrounded by black;
and on the brown, red, and yellow tints present in this spot during the
last stage, a nearly black spot has been developed--the pupil of the
eye (Fig. 33). In order to establish a definite terminology for the
different portions of the eye-spot, I shall designate the pupil as the
“nucleus,” the light ground on which the pupil stands as the “mirror,”
and the black ground which surrounds the mirror as the “ground-area.”
In this fifth stage the larva attains a length of six centimeters,
after which the fifth moult takes place, the caterpillar becoming ready
for pupation in the sixth stage. No striking changes of colouring or
marking occur after the present stage, but only certain unimportant
alterations, which are, however, of the greatest theoretical interest.
_Sixth Stage._
In this stage the eye-like appearance of the spots on the front
segments becomes still more distinct than in the fifth stage; at the
same time these spots repeat themselves on all the other segments from
the fifth to the eleventh, although certainly without pupils, and
appearing only as diffused, deep black spots, of the morphological
significance of which, however, there cannot be the least doubt. They
are situated in precisely the same positions on the 5-11 segments as
those on the third and fourth--near the front, and above and below
the subdorsal line. A feeble indication of the latter can often be
recognized (Fig. 23).
In all dark brown specimens the repeated spots can only be detected in
a favourable light, and after acquiring an intimate knowledge of the
caterpillar; but in light brown and green specimens they appear very
sharply defined.
There is one other new character which I have never observed at an
earlier period than the sixth stage, viz. the small dots which
appear in pairs near the posterior edge of segments 5-11. These dots
cannot have been developed from the subdorsal line, as they are
situated higher than the latter. Their colour varies according to the
ground-colour of the caterpillar, but it is always lighter, being light
green in green specimens, dull yellow in those that are light brown,
and grey in the blackish-brown caterpillars. These “dorsal spots,” as
I shall term them, are chiefly of interest because they are present in
_Chærocampa Porcellus_, in which species they appear one stage earlier
than in _C. Elpenor_.