an unusual
development in the organs of touch.

But it is none the less certain that the presence of this light cannot
always be designed to serve this purpose, for many of the animals so
endowed are blind. The phosphorescent centipedes are without eyes,
like all the other members of the genus (_Geophilus_) to which they
belong, and probably the majority of phosphorescent marine forms are
likewise destitute of organs of sight.

Another suggestion is that the light derived from these marine forms,
and especially from deep-sea Alcyonarians, is what enables the members
of the deep-sea fauna that are possessed of eyes (which are always
enormously enlarged) to see. Such is the suggestion of Dr. Carpenter,
Sir Wyville Thomson, and Mr. Gwyn Jeffries; and it is possible that
this actually is one of the effects of the phosphorescent property.
But if so, it remains to inquire how the forms endowed with it came
to be possessed of a power useful in that way to other forms, but not
to themselves. According to the Darwinian doctrine of development, the
powers that are developed in different organisms by the process of
natural selection are such as are useful to themselves and not to
others, unless incidentally.

This consideration has led to another suggestion, namely, that the
property of phosphorescence serves as a protection to the forms
possessing it, driving away enemies in one way or another: it may be
by warning them of the fact that they are unpalatable food, as is
believed to be the case with the colors of certain brilliantly-colored
caterpillars; it may be in other ways. In Kirby and Spence one case is
recorded in which the phosphorescence of the common phosphorescent
centipede (_Geophilus electricus_) was actually seen apparently to
serve as a means of defence against an enemy. "Mr. Shepherd," says
that authority, "once noticed a scarabeus running round the
last-mentioned insect when shining, as if wishing, but afraid to
attack it." In the case of the jelly-fishes, it has been pointed out
that their well-known urticating or stinging powers would make them at
least unpleasant, if not dangerous, food for fishes; and that
consequently the luminosity by which so many of them are characterized
at night may serve at once as a warning to predatory fishes and as a
protection to themselves. The experience of the unpleasant properties
of many phosphorescent animals may likewise have taught fishes to
avoid all forms possessing th