The Descent of Man

from specimens in the
British Museum, under the kind superintendence
of Dr. Gunther.]
Fig. 28. Head of female salmon.]
The most curious point about the male salmon
is that during the breeding- season, besides a
slight change in colour, "the lower jaw elongates,
and a cartilaginous projection turns upwards
from the point, which, when the jaws are
closed, occupies a deep cavity between the intermaxillary
bones of the upper jaw." (7. Yarrell,
'History of British Fishes,' vol. ii. 1836, p.
10.) (Figs. 27 and 28.) In our salmon this change
of structure lasts only during the breedingseason;
but in the Salmo lycaodon of N.W.
America the change, as Mr. J.K. Lord (8. 'The
Naturalist in Vancouver's Island,' vol. i. 1866, p.
54.) believes, is permanent, and best marked in
the older males which have previously ascended
the rivers. In these old males the jaw becomes
developed into an immense hook-like