The Evolution of Man, vol 1 | Page 5

pass roughly and rapidly
through a series of forms which represents the succession of their
ancestors in the past. After a severe and extensive study of embryonic
phenomena, Haeckel has drawn up a "law" (in the ordinary scientific
sense) to this effect, and has called it "the biogenetic law," or the chief
law relating to the evolution (genesis) of life (bios). This law is widely
and increasingly accepted by embryologists and zoologists. It is enough
to quote a recent declaration of the great American zoologist, President
D. Starr Jordan: "It is, of course, true that the life-history of the
individual is an epitome of the life-history of the race"; while a
distinguished German zoologist (Sarasin) has described it as being of
the same use to the biologist as spectrum analysis is to the astronomer.
But the reproduction of ancestral forms in the course of the embryonic
development is by no means always clear, or even always present.
Many of the embryonic phases do not recall ancestral stages at all.
They may have done so originally, but we must remember that the
embryonic life itself has been subject to adaptive changes for millions
of years. All this is clearly explained by Professor Haeckel. For the
moment, I would impress on the reader the vital importance of fixing
the distinction from the start. He must thoroughly familiarise himself
with the meaning of five terms.
BIOGENY is the development of life in general (both in the individual
and the species), or the sciences describing it.
ONTOGENY is the development (embryonic and post-embryonic) of

the individual (on), or the science describing it.
PHYLOGENY is the development of the race or stem (phulon), or the
science describing it.
Roughly, ontogeny may be taken to mean embryology, and phylogeny
what we generally call evolution.
Further, the embryonic phenomena sometimes reproduce ancestral
forms, and they are then called PALINGENETIC (from palin = again):
sometimes they do not recall ancestral forms, but are later
modifications due to adaptation, and they are then called
CENOGENETIC (from kenos = new or foreign).
These terms are now widely used, but the reader of Haeckel must
understand them thoroughly.
The first five chapters are an easy account of the history of embryology
and evolution. The sixth and seventh give an equally clear account of
the sexual elements and the process of conception. But some of the
succeeding chapters must deal with embryonic processes so unfamiliar,
and pursue them through so wide a range of animals in a brief space,
that, in spite of the 200 illustrations, they will offer difficulty to many a
reader. As our aim is to secure, not a superficial acquiescence in
conclusions, but a fair comprehension of the truths of science, we have
retained these chapters. However, I will give a brief and clear outline of
the argument, so that the reader with little leisure may realise their
value.
When the animal ovum (egg-cell) has been fertilised, it divides and
subdivides until we have a cluster of cohering cells, externally not
unlike a raspberry or mulberry. This is the morula (= mulberry) stage.
The cluster becomes hollow, or filled with fluid in the centre, all the
cells rising to the surface. This is the blastula (hollow ball) stage. One
half of the cluster then bends or folds in upon the other, as one might
do with a thin indiarubber ball, and we get a vase-shaped body with
hollow interior (the first stomach, or "primitive gut"), an open mouth
(the first or "primitive mouth"), and a wall composed of two layers of
cells (two "germinal layers"). This is the gastrula (stomach) stage, and
the process of its formation is called gastrulation. A glance at the
illustration (Figure 1.29) will make this perfectly clear.
So much for the embryonic process in itself. The application to
evolution has been a long and laborious task. Briefly, it was necessary

to show that ALL the multicellular animals passed through these three
stages, so that our biogenetic law would enable us to recognise them as
reminiscences of ancestral forms. This is the work of
Chapters
1.8 and 1.9. The difficulty can be realised in this way: As we reach the
higher animals the ovum has to take up a large quantity of yelk, on
which it may feed in developing. Think of the bird's "egg." The effect
of this was to flatten the germ (the morula and blastula) from the first,
and so give, at first sight, a totally different complexion to what it has
in the lowest animals. When we pass the reptile and bird stage, the
large yelk almost disappears (the germ now being supplied with blood
by the mother), but the germ has been permanently altered in shape,
and there are now a number of new embryonic processes (membranes,
blood-vessel connections, etc.). Thus