ars, which to-day show oblique stripes, possessed
longitudinal stripes in Tertiary times? We can read this fact from the
history of their development, and I have before attempted to show
the biological significance of this change of colour. ("Studien
zur Descendenz-Theorie" II., "Die Enstehung der Zeichnung bei den
Schmetterlings-raupen," Leipzig, 1876.)

For the present I need only draw the conclusion that one and the same
caterpillar may exhibit the initial stages of both, and that it depends
on the manner in which these marking elements are INTENSIFIED and
COMBINED by natural selection whether whitish longitudinal or oblique
stripes should result. In this case then the "useful variations"
were actually "always there," and we see that in the same group of
Lepidoptera, e.g. species of Sphingidae, evolution has occurred in both
directions according to whether the form lived among grass or on broad
leaves with oblique lateral veins, and we can observe even now that the
species with oblique stripes have longitudinal stripes when young, that
is to say, while the stripes have no biological significance. The white
places in the skin which gave rise, probably first as small spots,
to this protective marking could be combined in one way or another
according to the requirements of the species. They must therefore either
have possessed selection-value from the first, or, if this was not
the case at their earliest occurrence, there must have been SOME OTHER
FACTORS which raised them to the point of selection-value. I shall
return to this in discussing germinal selection. But the case may be
followed still farther, and leads us to the same alternative on a still
more secure basis.

Many years ago I observed in caterpillars of Smerinthus populi (the
poplar hawk-moth), which also possess white oblique stripes, that
certain individuals showed RED SPOTS above these stripes; these spots
occurred only on certain segments, and never flowed together to form
continuous stripes. In another species (Smerinthus tiliae) similar
blood-red spots unite to form a line-like coloured seam in the last
stage of larval life, while in S. ocellata rust-red spots appear in
individual caterpillars, but more rarely than in S. Populi, and they
show no tendency to flow together.

Thus we have here the origin of a new character, arising from small
beginnings, at least in S. tiliae, in which species the coloured stripes
are a normal specific character. In th