200 THE ANIMALS AND MAN 



cultivated has not been able naturally to reach. The eggs 

 of some fishes are large and non-adherent, two features 

 which greatly favor artificial impregnation and hatching. 

 In the hatcheries the eggs are put first into warm water, 

 where development begins; they are then removed into cool 

 water, which arrests development without injury, making 

 shipment possible. The eggs of salmon and trout in par- 

 ticular can be" sent long distances to suitable streams or 

 ponds. The eggs of the shad have been thus carried from 

 the East to the streams of California, and trout have been 

 distributed to many streams in our country which by them- 

 selves they could never have reached. 



The salmon is a conspicuous example of those fishes which 

 can be artificially propagated. The eggs of the salmon are 

 large, firm, and separate from each other. If the female fish 

 be caught when the eggs are ripe and her body be pressed 

 over a pan of water the eggs will flow out into the water. By 

 a similar process the milt or male sperm-cells can be pro- 

 cured and poured over the eggs to fertilize them. The young 

 after hatching are kept for a few days or weeks in artificial 

 pools till the yolk-sacs are absorbed and they can take care 

 of themselves. They are then turned into the stream, where 

 they drift tail foremost with the current and pass downward 

 to the sea. All trout may be treated in similar fashion, but 

 there are many food-fishes which cannot be handled in this 

 way. In some the eggs are small or soft, or viscid and ad- 

 hering in bunches. In others the life-habits make artificial 

 fertilization impossible. Such species are artificially reared 

 only by catching the young and taking them from one stream 

 to another. To this type belong the black bass, the sunfish, 

 the catfish and other familiar forms. 



Baskett's "Story of the Fishes," McCarthy's "Familiar Fish," and 

 Jordan and Evermann's "Food and Game Fishes of America" are good 

 books for elementary students of fishes. 



The batrachians. — We have made the acquaintance of 



