THE FISHES 



I6 3 



trom its mouth. During their course the males become 

 lean and battered, and they acquire a peculiar lengthening 

 of the lower jaw and an increased development of teeth 

 which are of value in their frequent combats with others 

 of their own sex. When the fishes finally arrive at a suita- 

 ble breeding place in some shallow stream, the eggs are 

 laid and fertilized, after which the life of the parent fish 

 is short. Thenceforth, the mission of their long and peril- 

 ous journey accomplished, they live only in their posterity. 



FIG. 131. Stripping fish to obtain the eggs. 



The young salmon gradually works down stream, grow- 

 ing in the meantime from its diet of worms, flies and other 

 small creatures, and finally reaches the ocean where it 

 lives until it in turn comes to obey the mysterious call to 

 enter the river and sacrifice itself for the perpetuation 

 of the species. 



The migration of the common eel Anguilla is the reverse 

 of that of the salmon, for the adults go down the rivers 

 to breed in the ocean and the young migrate up the streams 

 and live for most of their lives in fresh water. 



As the eggs of nearly all food fishes are fertilized outside 



