The Descent of Man

veloped later in life in this breed than in ordinary
sheep in which both sexes are horned. But
with domesticated sheep the presence or absence
of horns is not a firmly fixed character;
for a certain proportion of the merino ewes
bear small horns, and some of the rams are
hornless; and in most breeds hornless ewes are
occasionally produced.
Dr. W. Marshall has lately made a special study
of the protuberances so common on the heads
of birds (43. 'Uber die knochernen Schadelhocker
der Vogel,' in the 'Niederland. Archiv fur
Zoologie,' B.i. Heft 2, 1872.), and he comes to
the following conclusion:—that with those species
in which they are confined to the males,
they are developed late in life; whereas with
those species in which they are common to the
two sexes, they are developed at a very early
period. This is certainly a striking confirmation
of my two laws of inheritance.