author.

The main theme of the work is that, in the course of their embryonic
development, all animals, including man, 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.