_F_+_f_ and _f_+_f_

and the fertilisations

_Ff_ and _ff_,

or males and females in equal numbers, as they are, at least
approximately, in fact.

The close agreement of this theory with what actually happens is certainly
important and suggests that it contains some truth. But it cannot be said
to be a satisfactory explanation. It ignores the question of the nature of
sex. According to the theory the female character is entirely wanting in
the male. But what is sex but the difference between ovum and
spermatozoon, between megagamete and microgamete? The theory then asserts
that an individual developed from a cell formed by the union of male and
female gametes is entirely incapable of producing female gametes again.
Every zygote after conjugation or fertilisation may be said to be bisexual
or hermaphrodite. How comes it then that the female quality entirely
disappears? Whether the gametocytes are distinguishable at an early stage
in the segmentation of the ovum, or only at a later stage of development,
we know that the gametes ultimately formed have descended by a series of
cell-divisions from the fertilised ovum or zygote cell from which
development commenced. If segregation takes place at the reduction
divisions we might suppose that half the gametes formed are sperms and
half are ova, and that in the male the latter do not survive but perish
and disappear. But in this case it would be the whole of the chromosomes
coming from the original female gamete which would disappear, and the
spermatozoon would be incapable of transmitting characters derived from
the female parent of the individual in which the spermatozoa were formed.