194 BRITISH FRESH-WATER FISHES 
(see page 158). A more probable explanation of the change 
of skin colour which takes place after the salmon enters fresh 
water will be submitted in the next chapter. In most 
teleosteous fish—the carps and pike, for instance — the 
beauty of colour culminates at the spawning season, as if 
the different sexes took pleasure in the brilliancy of each 
other. It is difficult, for instance, to imagine a female 
stickleback of so phlegmatic a nature as not to derive 
excitement from the bridal raiment of her spouse. But 
salmon, male and female, so far from acquiring enhanced 
comeliness at this critical season, become positively unsightly. 
The male turns to a deep coppery brown; the burnished 
silver of his mate is deeply tarnished with exactly the same 
tints as sulphurous fumes impart to the real metal. Her 
snowy throat and underparts are smeared and stained with 
the same sooty hue, and her once perfect form distended by 
the swollen ovaries. Both sexes lose their crispness to the 
touch, and become covered with slime. 
As if this disguise were not enough, the male assumes 
as it were an ugly mask. When salmon of less than 10 lb. 
or 12 lb. in weight leave the sea the heads of the two sexes 
are indistinguishable from each other;* but as the milt 
grows in the male so do his snout and lower jaw, and at 
the end of the lower jaw a knob grows upon the upper 
edge of the mandible, forming a pronounced hook, which, 
in old males, fits into a recess in the snout when the mouth 
is closed. This characteristic hook is neither cartilaginous 
nor bony, but is formed entirely of cutaneous connective 
* Tam quite aware that experienced fishermen profess to distinguish 
between newly-run male and female fish by the shape of their jaws, but I 
have adduced evidence on page 237 to show that it is impossible to do 
so early in the season, before the generative apparatus of the fish has 
advanced towards maturity. It is difficult, perhaps impossible, to convince 
fishermen of this, and indeed in very o/d ma/es the base of the temporary 
hook formed on the mandible becomes bony, and the jaws remain longer 
than those of females, thereby affording a permanent indication of sex. 
