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their many editions. We may assume that it is well known, and need only
briefly recall its chief characteristics. The "inestimable value," the
"incomparable significance," the "immeasurable importance" of the Theory
of Descent lies, according to Haeckel, in the fact that by means of it we
can explain the origin of the forms of life "in a mechanical manner." The
theory, especially in regard to the descent of man from the apes, is to
him not a working hypothesis or tentative mode of representation; it is a
result comparable to Newton's law of gravitation or the Kant-Laplace
cosmogony. It is "a certain historical fact." The proofs of it are those
already mentioned.

What is especially Haeckelian is the "fundamental biogenetic law,"
"ontogeny resembles phylogeny," that is to say, in development, especially
in embryonic development, the individual recapitulates the history of the
race. Through "palingenesis," man, for instance, recapitulates his
ancestral stages (protist, gastraead, vermine, piscine, and simian). This
recapitulation is condensed, disarranged, or obscured in detail by
"cenogenesis" or "caenogenesis." The groups and types of organisms exhibit
the closest genetic solidarity. The genealogical tree of man in particular
runs directly through a whole series. From the realm of the protists it
leads to that of the gastraeadae (nowadays represented by the Coelentera),
thence into the domain of the worms, touches the hypothetical "primitive
chordates" (for the necessary existence of which "certain proofs" can be
given), the class of tunicates, ascends through the fishes, amphibians and
reptiles to forms parallel to the modern monotremes, then directly through
the marsupials to the placentals, through lemuroids and baboons to the
anthropoid apes, from them to the "famous Pithecanthropus" discovered in
Java, out of which _homo sapiens_ arose. (The easy transition from one
group of forms to another is to be noted. For it is against this point
that most of the opposition has been directed, whether from "grumbling"
critics, or thoroughgoing opponents of the Theory of Descent.)

Haeckel's facile method of constructing genealogical trees, which ignores
difficulties and discrepant facts, has met with much criticism and
ridicule even among Darwinians. The "orator of Berlin," Du Bois-Reymond,
declared that if he must read romances he would prefer to read them in
some other form than that of genealogical trees. But they have at