THE SALMON FAMILY 51 
We have presumed that all has gone well with the 
eggs left in the gravel, but in nature only a small per- 
centage of the eggs deposited result in the birth of an 
alevin. Sometimes the eggs are insufficiently covered, 
and being washed out of the redds, they are quickly 
devoured by young trout, always to be found on the 
spawning grounds. Late spawners frequently expose 
the eggs already deposited, and indulge in a hearty meal. 
Ducks, water hens, rats, eels, insects and larve all take 
their share of the spoil. Floods may cause countless ova 
to be buried feet deep under gravel and debris; or if 
the water shrinks, the eggs may be left high and dry. 
Finally, in a cold winter the water over the redds may 
freeze solid, and when the ice moves it takes with it 
gravel, buried eggs and all. 
Now, to return to the newly-hatched alevin. It will 
be seen that a continuous primitive fin runs right round 
the body, but notice there are irregularities where the 
permanent fins will appear. The gill clefts are clearly 
shown, and attached to the little fish is the huge yolk 
sac from which it derives its nourishment for five or 
six weeks. 
The left side of the yolk sac is seen in the illustra- 
tion of the salmon just hatched. The dark mass at the 
upper part is the liver, which is of a deep salmon pink 
colour; the round objects are oil globules, and the net- 
work over the yolk sac is a mass of small blood-vessels. 
In the photograph of the alevin with its head just 
hatched, the heart is clearly seen, and the curved dark 
