enabled by means of them to bore rapidly into the ground and so to escape
from enemies. We do not know what the initial stages were, but we cannot
doubt that the little improvements, which occurred as variations of the
originally simple slimy bodies of the Holothurians, were preserved because
they already possessed selection-value for the Synaptidae. For such minute
microscopic structures whose form is so delicately adapted to the role they
have to play in the life of the animal, cannot have arisen suddenly and as
a whole, and every new variation of the anchor, that is, in the direction
of the development of the two arms, and every curving of the shaft which
prevented the tips from projecting at the wrong time, in short, 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