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 larvae 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 



