arious forms of animals
have proceeded directly from one another. My hypothesis of the creation
of organisms by heterogeneous generation, however, is distinguished
very essentially from Darwin's by the entire absence of the principle
of useful variations and their natural selection: and my fundamental
conception is this, that a great plan of development lies at the
foundation of the origin of the whole organic world, impelling the
simpler forms to more and more complex developments. How this law
operates, what influences determine the development of the eggs and
germs, and impel them to assume constantly new forms, I naturally cannot
pretend to say; but I can at least adduce the great analogy of the
alternation of generations. If a 'Bipinnaria', a 'Brachialaria', a
'Pluteus', is competent to produce the Echinoderm, which is so widely
different from it; if a hydroid polype can produce the higher Medusa;
if the vermiform Trematode 'nurse' can develop within itself the very
unlike 'Cercaria', it will not appear impossible that the egg, or
ciliated embryo, of a sponge, for once, under special conditions, might
become a hydroid polype, or the embryo of a Medusa, an Echinoderm."

It is obvious, from these extracts, that Professor Kolliker's hypothesis
is based upon the supposed existence of a close analogy between the
phenomena of Agamogenesis and the production of new species from
pre-existing ones. But is the analogy a real one? We think that it is
not, and, by the hypothesis, cannot be.

For what are the phenomena of Agamogenesis, stated generally? An
impregnated egg develops into an asexual form, A; this gives rise,
asexually, to a second form or forms, B, more or less different from A.
B may multiply asexually again; in the simpler cases, however, it does
not, but, acquiring sexual characters, produces impregnated eggs from
whence A, once more, arises.

No case of Agamogenesis is known in which, 'when A differs widely from
B', it is itself capable of sexual propagation. No case whatever is
known in which the progeny of B, by sexual generation, is other than a
reproduction of A.

But if this be a true statement of the nature of the process of
Agamogenesis, how can it enable us to comprehend the production of
new species from already existing ones? Let us suppose Hyaenas to have
preceded Dogs, and to have produced the latter in this way. Then the
Hyena will represent A, and the Dog, B. The first difficulty that
presen