854 
SCANDINAVIAN FISHES. 
the rostral region), which may be persistent in Salmon 
normal in all other respects, and admits of quite a 
considerable development (tig. 213). 
The Salmon leads a life full of changes, and it 
adapts itself to them both in form and colouring. The 
form undergoes the same variations as in the Charr, 
but is never so terete as it may sometimes be in the 
latter. Most terete, most nearly fusiform, though always 
laterally compressed, is the true Salmon in its sea- 
dress, with broad, convex back and sometimes with 
the greatest thickness of the body equal to two-thirds 
of its greatest depth, which is then about one-fifth of 
the length to the middle of the base of the caudal fin. 
The difference from the Trout in the same dress is, 
however, inconstant and sometimes absent; and in the 
a 
Fig. 2 13. Monstrous head (simous malformation) of a Salmo salar 
a, from the left; b, from in front. T 
spawning-dress they both assume a deeper and thinner 
form of body. This is especially prominent in old 
males; which during the spawning- season develop, be- 
sides the singular jaw-hook, to which we shall return 
below, a high and more or less sharp dorsal projection 
in front, supported internally by an indurated connec- 
tive tissue. This hump, however, in no instance attains 
the same development in the Salmons as in Charr of 
the Oncliorliynchus group". Where the true Salmon 
lives confined in fresh water, as in Lake Wener, it 
also acquires as a general rule a deeper, more com- 
pressed form; and that the Kelts (spent Salmon) have 
a thinner body, we have already remarked. During 
the earlier stages the distinction between Salmon and 
a See Smitt, EiJcsmuseets Salmonider , tail. Ill, fig. 28. 
6 In Parrs. 
c In the largest breeding males of the typical Salmon which 
Trout is, as a rule, more evident in the above respect: 
it is generally easy to distinguish by the form young 
Salmon (blanklax-foreller) from young Trout ( foreller ), 
the body of the former being shallower, with the 
greatest depth less than one-fifth of the length. At 
this stage, however, the difference is most marked in 
the more or less forked shape of the caudal fin: in 
young Salmon the length of the middle caudal rays is 
less, in young Trout more, than half that of the long- 
est rays in the fin. As appears from the table of 
averages on the preceding page, this character is in- 
deed persistent, in typical specimens of the two varie- 
ties, even in later life; but it disappears in old Sal- 
mon wearing the spawning-dress, and sterile Trout 
have a caudal fin most like that of typical Salmon. 
b 
nernensis, taken by Mr. Datjlgrun in 1880. 1 / 2 of the natural size; 
specimen probably measured 7 — 8 dm. 
Among the changes of growth that most contri- 
bute to modify the appearance of the Salmons, the 
most striking are those which affect the form of the 
snout. In young Salmon the snout is comparatively 
short and blunt; but its length sometimes increases 
with age from about 5 % h to about 13 % c of that of 
the body, or from about 21 % h to 47 % c of that of 
the head reduced. This prolongation mainly affects 
the anterior, pramasal part, the nostrils remaining at 
a distance from the anterior orbital margin which in 
young specimens is less, in old only slightly greater, 
than the diameter of the eyes. The elongation pro- 
ceeds uniformly in the females and the middle-sized 
males, where the snout acquires a more or less point- 
ve have been enabled to examine. 
