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 lies in the fact that the former can modify only a
few characters, usually only one at a time, while Nature preserves in the
struggle for existence all the variations of a species, at the same time
and in a purely mechanical way, if they possess selection-value.

Herbert Spencer, though himself an adherent of the theory of selection,
declared in the beginning of the nineties that in his opinion the range of
this principle was greatly over-estimated, if the great changes which have
taken place in so many organisms in the course of ages are to be
interpreted as due to this process of selection alone, since no
transformation of any importance can be evolved by itself; it is always
accompanied by a host of secondary changes. He gives the familiar example