152 NATURE-STUDY REVIEW [14:4— April, 1918 



cold, fresh water in the rivers, and seeming anxious to remain in 

 this cold water. 



They reach the mouths of the rivers, and here dally for some 

 time, as though at play, and not yet filled with any serious purpose. 

 This seeming play is accounted for in this way. The general body 

 of the fish is built in such a manner that the fish can progress most 

 easily with its head against the current, and it is in this position 

 that the salmon are found in their progress up the rivers. But in 

 the mouths of the rivers are two conflicting currents, the ebb tide 

 and the flood tide. When the tide ebbs out the fish journey against 

 the current up the river, but before they have gone far the full tide 

 overtakes them, and obeying the instinct to head against the cur- 

 rent, they face about again toward the sea. Each day they pro- 

 gress a little farther up the river, and finally get above the point 

 reached by the tides from the ocean. 



When they finally really start up the river, their progress is 

 much faster. Salmon on the way to the spawning grounds do not 

 feed. Many investigations show that the pyloric orifice of the 

 stomach shrinks decidedly, so that the fish cannot feed. More- 

 over, in the males, both the premarillaries and the tip of the lower 

 jaw have been gradually more and more prolonged, till the jaws 

 either shut from side to side like a pair of shears or else the mouth 

 cannot be closed at all. While salmon will occasionally take bait 

 or flies at this stage of their journey, it does not seem to be because 

 they are hungry, but rather because the bobbing object irritates 

 them to a point of recklessness. Should you see the salmon now, 

 you certainly would hardly recognize it as the same fish that was 

 sporting about in the ocean a few short months ago. In the males 

 the peculiar changes in the jaws occur, while the teeth on the tongue 

 and vomer often disappear entirely ; the body becomes compressed, 

 and deeper at the shoulders; a distinct hump is formed at the 

 shoulders; the scales disappear, giving place to a spongy growth of 

 skin; the color changes to black and red or blotched. The flesh 

 of both sexes is now inclined to be streaked or very pale pink, owing 

 to the loss of oil. This is true more especially of the salmon of the 

 fall running:. As the spawning season approaches, the females also 

 change much in appearance. They lose their silvery color, become 

 more slimy, the scales on the back sink into the flesh. These 

 changes in both male and female are due to the growth of the repro- 

 ductive organs. It is probable that these organs are not far 

 developed when the salmon first enter the river mouths. 



