ort, every little adaptation
in the modelling of the anchor must have possessed selection-value. And
that such minute changes of form fall within the sphere of fluctuating
variations, that is to say, THAT THEY OCCUR is beyond all doubt.

In many of the Synaptidae the anchors are replaced by calcareous rods
bent in the form of an S, which are said to act in the same way. Others,
such as those of the genus Ankyroderma, have anchors which project
considerably beyond the skin, and, according to Oestergren, serve "to
catch plant-particles and other substances" and so mask the animal. Thus
we see that in the Synaptidae the thick and irregular calcareous bodies
of the Holothurians have been modified and transformed in various ways
in adaptation to the footlessness of these animals, and to the peculiar
conditions of their life, and we must conclude that the earlier stages
of these changes presented themselves to the processes of selection in
the form of microscopic variations. For it is as impossible to think of
any origin other than through selection in this case as in the case of
the toughness, and the "drip-tips" of tropical leaves. And as these
last could not have been produced directly by the beating of the heavy
rain-drops upon them, so the calcareous anchors of Synapta cannot have
been produced directly by the friction of the sand and mud at the bottom
of the sea, and, since they are parts whose function is PASSIVE the
Lamarckian factor of use and disuse does not come into question. The
conclusion is unavoidable, that the microscopically small variations of
the calcareous bodies in the ancestral forms have been intensified
and accumulated in a particular direction, till they have led to the
formation of the anchor. Whether this has taken place by the action
of natural selection alone, or whether the laws of variation and the
intimate processes within the germ-plasm have cooperated will become
clear in the discussion of germinal selection. This whole process of
adaptation has obviously taken place within the time that has
elapsed since this group of sea-cucumbers lost their tube-feet, those
characteristic organs of locomotion which occur in no group except the
Echinoderms, and yet have totally disappeared in the Synaptidae.
And after all what would animals that live in sand and mud do with
tube-feet?

(c) COADAPTATION.

Darwin pointed out that one of the essential differences between
artificial and natural selection li