NATURAL HISTORY OF BRITISH SALMONIDA. 135 
by ascending thus early, before their spawn is at all matured, 
are vigorous, and able to overcome the obstacles in their upward 
course to the extreme sources of the river—to which those fish 
remaining in the sea until heavy with spawn could never pene- 
trate. 
Curiously enough, an analogous fact has been noticed witk 
regard to the spawning of the common trout. Dr. Davy, who 
was in the habit of opening the fish he caught, records that by 
this means he discovered that, as the spawning season ap- 
proached, only about one-half of the females had visible eggs, 
whilst in the other half there were xo signs of the development of 
the ova. Charr, also, are frequently taken in Windermere in 
high condition in October and November, which is their regular 
spawning season—a fact which would seem to point to the pos- 
sibility of the rule of alternate spawning years holding good in 
the case of all the fish of the salmon and trout species. 
But to return. The ascent of salmon to the spawning 
grounds is usually somewhat in this wise. During the early part 
of the season, the fish in the rivers, which do not at once 
ascend, remain in or near the mouths. But with the advance 
of the season they get gradually farther into the fresh water 
beyond the influence of the sea. The edible quality of the 
salmon when thus ascending rivers depends entirely upon the 
state of development of the milt or roe—a loss of condition, 
accompanied by the usual change of colour, following, even in 
the salt water, upon the maturing of the spawn. The efforts of 
the salmon to surmount all obstacles to their ascent of the 
rivers increase with the approach of the spawning time, and 
they shoot up rapids, and make wonderful exertions to surmount 
cascades and other impediments, frequently clearing a height 
of two or three yards at a bound. It has been calculated that, 
when swimming, or rather darting at full speed, the salmon will 
glide through the water at the rate of about 1,500 ft. per minute, 
or upwards of 400 miles per day—a pace which, if it could 
be maintained, would speedily carry the fish round the world. 
Although the height to which a salmon will leap seems 
