is is true both as to appearance and as to behaviour.
Some of these were quite nearly males in appearance and behaviour,
though they laid eggs.

Testicular and ovarian extracts were injected. The more feminine birds
were often killed by the testicular extract, the more masculine by the
ovarian extract. Finally, to make assurance doubly sure, some females
which should theoretically have been the most feminine were dissected
and shown to be so. That is, out-crosses which produced a predominance
of females in the fall were mated with females which had been overworked
at egg production until they threw nearly all females. Dissecting the
females thus produced, they were shown to have _right ovaries_, which
means _double femaleness_, since normally the pigeon is functional only
in the left ovary, like other birds. The right one usually degenerates
before or at hatching and is wholly absent in the week-old squab.

In pigeons, Riddle thinks the "developmental energy" of the eggs is in
an inverse ratio to their size. The last and largest eggs of the season
develop least and produce most females. The second egg of a clutch is
larger than the first, but develops less and the bird produced is
shorter-lived. Overworking and other conditions tending to produce large
eggs and females also throw white mutants and show other signs of
weakness. Old females lay larger eggs than do young ones. These eggs
produce more females. They store more material, have a lower metabolism
and less oxidizing capacity than do the earlier male-producing eggs.

It would be unsafe to draw specific conclusions about mammals from these
bird and insect experiments. Both the secretory action and the
chromosome mechanisms are different. The quantitative nature of sex, and
also the existence of intersexual types, between males and females,
would seem to be general phenomena, requiring rather slight
corroboration from the mammals themselves. We have such mammalian cases
as the Free-Martin cattle, and some convincing evidence of
intersexuality in the human species itself, which will be reviewed
presently.

The notion of more "developmental energy" or a higher metabolism in
males is borne out in the human species. Benedict and Emmes[7] have
shown by very careful measurements that the basal metabolism of men is
about 6% higher than that of women. Riddle cites the work of Thury and
Russell on cattle to show that a higher water value (as he found in the
pigeon eggs)