Life of the Waters 361 



produces one of the principal industries of the Pacific Coast, 

 while the migration of the shad in the rivers of the Atlantic 

 Coast, in former days brought wealth to the fisherman, and 

 delight to the palates of those fortunate enough to feast on 

 this delicious food. Now unfortunately owing to various 

 factors this fishery is much decreased. 



The underlying cause of these breeding migrations of fish 

 is still as much an unsolved problem as is that of bird migra- 

 tion. We have already seen the profound influence which 

 internal secretions exercise upon the metabolism and growth 

 of animals. We have also seen how external chemical agents 

 may influence the reactions of animals (i. e., light responses 

 of Daphnia, etc.). The cause therefore of these movements 

 of certain fish is undoubtedly to be sought in the action of 

 a secretion of the sex glands causing primarily restlessness 

 and movement from place to place on the part of the fish, 

 and secondarily a change in response to the chemical environ- 

 ment. Thus the ripening cf the sex cells in an adromous fish 

 such as salmon and shad with the coincident formation of 

 some internal secretion by the 'sex glands, probably induces 

 restless wanderings on the part of the fish, in the course of 

 which they come into regions of fresh water discharged by 

 some river. Turning in the direction whence the fresh water 

 comes, they are guided to the mouth of the river, which they 

 ascend, due to their inclination to swim against the current. 

 The restlessness which brings them originally into fresher 

 water finds further expression in the leaping of the salmon 

 when they encounter a fall on their course up stream. This 

 instinct develops even in fish which have been kept from 

 birth to maturity in ponds, for such salmon have been known 

 to leap out of the water onto the bank to die. 



After spawning and cessation of the internal secretion the 

 fish lose their tendency to swim up stream, and are either 

 carried helplessly down by the current, dying as they go, 

 in the case of the adult salmon on our Pacific Coast, or in tne 

 case of the young salmon and the young and adults of other 

 fish (sturgeon, shad and Penobscot salmon) they swim with 

 the current back to their home in the sea. 



Eels have a different history, living in fresh waters and 

 descending the rivers to the sea to spawn. The mysterious 

 habits of the eel have given rise to some very curious tales of 

 early writers, according to whom eels are spontaneously 

 generated in mud and elsewhere, or are formed from horse 

 hair, old eel-skins, etc. After spending several years in fresh 

 water, the ripening of the sex organs probably induces the 

 wandering habit in the eel, and it descends the river to the 

 ocean, where it spawns in realms unknown, but in any event 



