surface absolutely unrelated. So the caterpillar
and the butterfly, to the naive child, seem as far apart as worm and
bird. In the case of the frog, the tadpole as a first sketch seems
completely an impossible and wild absurdity. Yet we know that there is
an orderly progression of events, a propagation of cells, a forward
going arrangement of chemical reactions, that results in expansion and
intricate complication of the organism. Just what the forces at work
in this most mysterious of all natural processes are, has been an
intellectual mystery that the best minds of the race have attempted
to get rid of with words like pangenesis (Darwin). Words of Black
(Mediterranean or Greek and Latin) origin, as Allen Upward has named
them, always cover a multitude of ignorances. The glands of internal
secretion, here, as in so many other dark places, provide the open
sesame to certain long closed doors of biology. They offer themselves
to us as the first definitely tangible agents which are known to keep
the process of growth going, and undoubtedly initiate the marvelous
unfolding of tissues and functions, organs and faculties summed up as
development or differentiation.

Thus by the direct feeding of thyroid at particular points in the
differentiating history most curious effects have been elicited. If
the gland is made part of the nutriment, the bathing environment, of
the tadpole, a hastening of its metamorphosis is attained. The tadpole
lives not out its day as a tadpole, but precociously turns into a
frog. But such a frog! It is a miniature frog, a dwarf frog, a frog
seen by looking through the wrong end of the telescope, a frog not
magnified, but micrified. Frogs have been so created the size of
flies. There has occurred a splitting of the two reactions which
ordinarily go hand in hand: the reaction of growth which is just brute
increase of total mass or weight and volume, and the reaction of
differentiation which is the finer process. The picture is a frog, but
a frog the size of a tadpole, a frog which has missed its childhood,
adolescence and youth, skipping over these transition stages into the
adult age, as a pigmy.

It is all as if a baby were suddenly to grow a beard and moustache,
evolve and shed teeth, and acquire the manner of an earnest citizen,
and yet retain the height and weight of a baby. That the spectacle
of such a superbaby is not quite the most fantastic of all
improbabilities is shown by the condition