irtue of that very regularity the problem is limited in scope and thus
simplified.

To begin with, we must relegate Selection to its proper place. Selection
permits the viable to continue and decides that the non-viable shall
perish; just as the temperature of our atmosphere decides that no liquid
carbon shall be found on the face of the earth: but we do not suppose
that the form of the diamond has been gradually achieved by a process of
Selection. So again, as the course of descent branches in the successive
generations, Selection determines along which branch Evolution shall
proceed, but it does not decide what novelties that branch shall bring
forth. "La Nature contient le fonds de toutes ces varietes, mais le
hazard ou l'art les mettent en oeuvre," as Maupertuis most truly said.

Not till knowledge of the genetic properties of organisms has attained
to far greater completeness can evolutionary speculations have more than
a suggestive value. By genetic experiment, cytology and physiological
chemistry aiding, we may hope to acquire such knowledge. In 1872
Nathusius wrote ("Vortrage uber Viehzucht und Rassenerkenntniss", page
120, Berlin, 1872.): "Das Gesetz der Vererbung ist noch nicht erkannt;
der Apfel ist noch nicht vom Baum der Erkenntniss gefallen, welcher,
der Sage nach, Newton auf den rechten Weg zur Ergrundung der
Gravitationsgesetze fuhrte." We cannot pretend that the words are not
still true, but in Mendelian analysis the seeds of that apple-tree at
last are sown.

If we were asked what discovery would do most to forward our inquiry,
what one bit of knowledge would more than any other illuminate the
problem, I think we may give the answer without hesitation. The greatest
advance that we can foresee will be made when it is found possible to
connect the geometrical phenomena of development with the chemical. The
geometrical symmetry of living things is the key to a knowledge of
their regularity, and the forces which cause it. In the symmetry of
the dividing cell the basis of that resemblance we call Heredity is
contained. To imitate the morphological phenomena of life we have to
devise a system which can divide. It must be able to divide, and to
segment as--grossly--a vibrating plate or rod does, or as an icicle can
do as it becomes ribbed in a continuous stream of water; but with
this distinction, that the distribution of chemical differences and
properties must simultaneously be decided and disposed in ord