Some Problems of Reproduction: a Comparative Study of ...

SOME PKOBLEMS OF REPRODUCTION. 71
no two such categories exist; on the contrary, all the evidence
goes to prove that a gamete of the A brood will pair with one
of any other brood from B to Z, and so on right through the
alphabet. Maupas has told us that for two Ciliates in the
eugamic state to pair successfully they must belong to two
different cycles of descent—that is, they must be descended
from two different exconjugates. If we use the term sex for
such cases as these we must admit the existence of as many
sexes as there are broods or cycles of the species in existence,
and that difference of sex means not a binary antithesis of
characters, but a mere question of kinship, which is a reductio
ad absurdum.
We see, then, that exogamy is merely the expression of consanguineous
incompatibility, or allogamy, as it has been long
termed. So far from indicating latent sex, allogamy may
or may not coexist with very high binary sexual differentiation.
In Orchids, for instance, side by side with the majority of
flowers adapted for cross-fertilisation exclusively, we find one
or two species that are " autogamous" or self-pollinating.
If we call allogamy by the name of " sex," it is a sex superimposed
on ordinary binary sex, and distinct from it; and the
question occurs here, in an allogamous species, How many
sexes are we to ascribe to the innumerable individuals, each
incapable of self-pollination, but capable of fertilising the flower
of any other individual?
We must remember, too, that in many isogamous forms, even
those which are exogamous, like Acetabularia, conjugation
may be multiple, as many as five gametes uniting into the
single zygote. Admitting the supposition that exogamy involved
latent binary sex, what would be the several functions
of each of these five gametes? The only conclusion left us is
the one we have stated, that exogamy expresses not an early
form of sexuality, but a growing sensibility of the organism to
the fact that the advantages of karyogamy are not fully gained
by the union of closely allied gametes j and this fastidiousness
we find an increasing factor as we ascend the scale of karyogamic
unions.