Hitherto I have unfortunately been unable to obtain fertile eggs of
this species, so that I can say nothing about the first stage. The
latter would have been of interest, not only because of the marking,
but also because of the presence of a residual caudal horn.
I am likewise only acquainted with the end of the second stage, having
found, at the end of June 1873, a single caterpillar on _Epilobium
Rosmarinifolium_, just previous to its second ecdysis. In the case of
such young caterpillars, however, the new characters which appear in
the succeeding stage are generally perceptible through the transparent
chitinous skin at the end of the preceding stage, so that the markings
of the insect are thus caused to change. The caterpillar found was
about 16 millimeters long, and of a beautiful smooth and shining
grass-green (Fig. 13). A broad white subdorsal line extended from the
first to the penultimate segment, from which the horn was completely
absent. On close inspection the first traces of the ring-spots could
be detected near the anterior edge of each segment as feeble, round,
yellow, ill-defined spots, situated on the subdorsal line itself (Fig.
13). On the first segment only there is no spot, and here no ring-spot
is afterwards formed. Besides these markings, there was only to be seen
a yellowish-white spiracular line.
This solitary specimen unfortunately buried itself before the moult
for which it had prepared itself had occurred; but this ecdysis is
associated with a very important transformation. This statement is
founded on a blown specimen in Staudinger’s collection; it is only
18 millimeters in length, but already shows the later grey colouring
in place of the beautiful green. In this, the third stage, the broad
white subdorsal line bears on each segment a red spot enclosed between
black crescents above and below (Fig. 49 A). In the fourth stage,
during which I have seen many living caterpillars, the subdorsal line
is still distinctly present in some individuals (Fig. 14), but the
spots (“mirrors”) are now completely surrounded by a narrow black
ring (“ground-area”), which sharply separates them from the subdorsal
line (Fig. 49 B). In the fifth stage this ring becomes a somewhat
irregularly formed black “ground-area,” whilst the subdorsal line
completely vanishes (Figs. 51 and 49 C). The mirrors are white, but
generally have a reddish nucleus, which obviously corresponds to the
primary yellow spots from which the whole development of the ring-spots
originates. This character is, however, sometimes absent; and many
other variations also occur in the earlier stages, all of which can be
easily explained as cases of arrested, or retarded development. Thus,
the subdorsal line often disappears earlier, and is only present in the
fourth stage as a feeble light stripe.