264 The Life Story of the Fish 



And so it may be seen that the eePs life-cycle is the re- 

 verse of the salmon's. The latter is born in fresh water, goes 

 to sea to live, feed, and grow, returns to fresh water to 

 spawn and die. The former is born in salt water, goes into 

 fresh water to live, feed, and grow, and returns to salt 

 water to spawn and die. It is difficult to conceive how the 

 salmon finds its way back from the sea to its home tribu- 

 tary; but it is even more difficult to conceive how the eel 

 finds its way back across the trackless ocean to the Sargasso 

 Sea. 



A very different kind of spawning migration is that of a 

 little smeltlike fish six inches long called the grunion. The 

 grunion lives along the sandy California beaches, and it has 

 worked out an equation in timing in which the movements 

 of the sun and the moon are the variables. 



The moon, as we all learned in school, is the principal 

 cause of the tides of the sea, but the sun also plays a part. 

 The moon moves in an orbit around the earth which it takes 

 a little more than twenty-nine days to complete. At one spot 

 in that orbit, the moon is directly on the line between the 

 earth and the sun, and the pull of moon and sun then com- 

 bine to make the tides higher than average. Some fourteen 

 days later, when the moon has gone half-way around the 

 earth, the moon is on the opposite side from the sun, and 

 the two astral bodies pull in opposite directions, with the 

 same result. In plain words, for the benefit of those not 

 astronomically minded, approximately every two weeks there 

 is a period of two or three days when the high tides are 

 higher than usual. These are called spring tides. At such 

 times, the waves come up on the beaches further than they 

 do at most high tides, and reach points on the sand which, 

 after their subsidence, will remain above water until the next 

 spring tides come two weeks later to wash over them again. 



The pressure of the life-force against its circumscribing 



