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
presents itself is that the Hyena must be asexual, or the process will
be wholly without analogy in the world of Agamogenesis. But passing over
this difficulty, and supposing a male and female Dog to be produced at
the same time from the Hyaena stock, the progeny of the pair, if the
analogy of the simpler kinds of Agamogenesis* is to be followed, should
be a litter, not of puppies, but of young Hyenas. ([Footnote] * If,
on the contrary, we follow the analogy of the more complex forms of
Agamogenesis, such as that exhibited by some 'Trematoda' and by the
'Aphides', the Hyaena must produce, asexually, a brood of asexual Dogs,
from which other sexless Dogs must proceed. At the end of a certain
number of terms of the series, the Dogs would acquire sexes and generate
young; but these young would be, not Dogs, but Hyaenas. In fact, we have
DEMONSTRATED, in Agamogenetic phenomena, that inevitable recurrence
to the original type, which is ASSERTED to be true of variations