qualitative but quantitative is probably nearer to the truth. Geddes and
Thomson and others have maintained that the sex-difference is one of
metabolism, the ovum being more anabolic, the sperm more katabolic. A
double quantity of special chromatin may be the cause of the greater
anabolism of the ovum. In that case the difficulty indicated in a previous
part of this chapter, that the ovum after reduction resembles the sperm in
having only one X chromosome, may be explained by the fact that the growth
of the ovum and its accumulation of yolk substances has been already
accomplished under the influence of the two chromosomes before reduction.
Other difficulties previously discussed also appear to be diminished if we
adopt this point of view. We need not regard maleness and femaleness as
unit characters in heredity of the same kind as Mendelian characters of
the soma. Instead of saying that the zygote composed of ovum and
spermatozoon is incapable of giving rise in the male to ova, or in the
female to sperms, we should hold that the gametocytes ultimately give rise
to ova or to sperms according to the metabolic processes set up and
maintained in them through their successive cell-divisions under the
influence of the double or single X chromosome. There still remains the
difficulty of explaining why the male gametocytes after reduction develop
into similar sperms, with their heads and long flagella, although half of
them possess one X chromosome each and the other half none. We can only
suppose that the final development of the sperms is the result of the
presence of the single X chromosome in the successive generations of male
gametocytes before the reduction divisions.

The Mendelian theory of sex-heredity assumed that in the reduction
divisions the two sex-characters, maleness and femaleness, were segregated
in the same way as a pair of somatic allelomorphs, but the words maleness
and femaleness expressed no real conceptions. The view above suggested
merely attempts to bring our real knowledge of the difference between ovum