The condition of affairs would be quite different if we were simply
concerned with the transference of a character from one segment
on which it was already present, to the remaining segments. The
transference would, in this case, result from causes purely innate in
the organism--from the action of laws of equilibration or of growth
(correlation), and the external conditions of life would play only a
negative part, since they might prevent the complete reproduction of
a character, such, for example, as eye-spots, on all the segments,
in cases where it was disadvantageous to the species. The fact that
our species of _Chærocampa_ have only faint indications, and not a
completely-developed eye-spot, on the remaining segments, may perhaps
be explained in this manner. It is conceivable that the two pairs
of ocelli on the front segments are more effective as a means of
alarm than if the insects were provided with two long rows of such
markings; but nothing can be stated with certainty on this point until
experiments have been made with caterpillars having rows of eye-spots.
The question raised above--whether the species of _Chærocampa_ at
present devoid of eye-spots are to be expected to acquire this
character in the course of their further phyletic development--brings
with it another point, which cannot be here passed over.
If the _utility_ of the four kinds of markings in their perfected form
is demonstrated, their origination through natural selection is not,
strictly speaking, thereby proved. It must also be shown that the first
rudiments of these characters were also of use to their possessors. The
question as to the utility of the “initial stages” of useful characters
must here be set at rest.
In the case of markings such as longitudinal and oblique stripes, it is
quite evident that the initial stages of these simple characters do not
differ greatly from the perfected marking, but this is certainly not
the case with eye- and ring-spots. The most light is thrown upon this
question by the latter, because a species which has remained at the
initial stage of the formation of ring-spots here presents itself for
examination, viz. _Deilephila Hippophaës_.
I have attempted to show that the orange-red spots, which, as a rule,
adorn only the eleventh segment, enhance the adaptive colouring of this
caterpillar by their resemblance to the berries of the sea-buckthorn,
whilst the general surface resembles the leaves in colour. If this be
admitted, the origination of these spots by natural selection offers no
difficulty, since a smaller spot, or one of a fainter red, must also be
of some use to its possessor.
Public-domain text, read in full here on John Shaqi.
Reviews
Reviews
No reviews yet
Be the first to share your thoughts on this work.
Elsewhere in the archive
Join the Discussion
Join the discussion
Sign in to leave a comment or review.
Sign InorCreate an account