NATURAL HISTORY OF BRITISH SALMONIDE. 124 
where they hatch in from eighty to one hundred and forty 
days, according to the temperature of the water. Eggs 
remaining unhatched beyond the latter period will seldom 
hatch at all. 
3. The eggs deposited by the female will not hatch under 
any circumstances unless vivified, after exclusion, by the milt 
of the male; and—at least up to the period of migration— 
there is no difference whatever in fry bred between salmon 
only, between grilse only, between salmon and grilse—between 
salmon and parr, or between grilse and parr. 
[Vote.—The female parr cannot spawn; but the male parr possesses, 
and constantly exercises, the power of vivifying salmon and grilse 
eggs. ] 
4. The fry remain one, two, and, in some cases, three 
years in the rivers as parr before going down to the sea—about 
half taking their departure at one year, nearly all the others at 
two years, and the remainder (which are exceptional) at three 
years old. 
5. All young salmon fry are marked with bluish bars on 
their sides until shortly before their migration, up to which 
period they are parrs ; they then invariably assume a more or 
less complete coating of silvery scales and become smolts— 
the bars, or parr marks, however, being still clearly discernible 
on rubbing off the new scales. 
6. The young of all the species of our salmon and trout, 
migratory and non-migratory, have at some period of their exist- 
ence these bluish bars ; and consequently such marks are not 
by themselves proofs that fry bearing them are the young of the 
true salmon (Salmo salar). 
7. Unless the young fish put on their smolt dress in May 
or early in June and thereupon go down to the sea, they 
remain as parrs another year ; and without smolt scales they 
will not migrate, and cannot exist in salt water. 
8. The length of the parr at six weeks old, is about an inch 
and a half or two inches; and the usual weight of the smolt 
before reaching the tidal wave from one to two ounces, 
