used in sexual combat, of copulatory or clasping organs such as the pads
on a frog's forefeet, of ornamental plumage like the peacock's tail
serving to charm the female, or of special pouches as in species of
pipe-fish and frog for holding the eggs or young. Darwin attempted to
explain sexual adaptation by sexual selection. The selective process in
this case was supposed to be, not the survival of individuals best adapted
to secure food or shelter or to escape from enemies, but the success of
those males which were victorious in combat, or which were most attractive
to the females, and therefore left the greater number of offspring which
inherited their variations. But, as Darwin himself admitted, this theory
of selection does not in any way explain the differences between the
sexes--in other words, the limitation of the characters or organs to one
sex--since there is no reason in the process of selection itself why the
peculiarity of a successful male should not be inherited by his female
offspring as well as by his male offspring. The real problem, then, is the
sex-limited heredity, and we shall consider later whether in this kind of
heredity also there are characters of internal as well as external origin,
blastogenic as well as somatogenic.



CHAPTER II

Mendelism And The Heredity Of Sex


We know that now individuals are developed from single cells which have
either been formed by the union of two cells or which develop without such
union, and that these reproductive cells are separated from pre-existing
organisms: the gametes or gonocytes are separated from the parents and