118 HERBERT SPENCER

to regenerate an amputated eye-bearing horn twenty
times in succession, a newt can replace a lost lens, a
lizard can regrow its tail and part of its leg, a stork
can regrow the greater part of its bill. In many
cases, the surrender of parts which are afterwards
regrown is exceedingly common, as in some worms
and Echinoderms, and is a life-saving adaptation.
Organically, though not consciously, the brainless
starfish has learned that it is better that one member
should perish than that the whole life should be lost.
This regenerative capacity no doubt implies certain
properties in the living matter and in the organism,
but we are far from being able to picture how it
comes about. What does seem clear is that the dis-
tribution and mode of occurrence of the regenerative
capacity—in external organs often, but in internal
organs very rarely; in most lizard's tails, but not in
the chamaeleon's; in the stork's bill but not in its toes
—are adaptive, being related to the normal risks of
life, as Reaumur, Lessona, Darwin, and Weismann
have pointed out. According to Lessona's Law,
which Weismann has elaborated, regeneration tends
to occur in those organisms and in those parts of
organisms which are in the ordinary course of nature
most liable to injury. To which we must add two
saving-clauses — (a) provided that the lost part is
of some vital importance, and (£) provided that the
wound or breakage is not in itself very likely to be
fatal. In Weismann's words, the theory is, that " the
power of regeneration possessed by an animal or by a
part of an animal is regulated by adaptation to the
frequency of loss and to the extent of the damage
done by the loss."n knownll in Development and