NA TURAL HISTOR Y OF BRITISH SALMONID^E. 127 



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. 



[Note. — 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. 



