430 



Biology in America 



the eggs and sperm have been taken they are mixed together 

 either in their natural condition or in a little water. The 

 eggs are then allowed to harden for an hour or so before 

 they are transferred to the hatching troughs. In this mixing 

 of eggs and sperm fertilization occurs, while the hardening 

 process renders them tougher and less liable to injury than 

 if they were transferred to the troughs directly after fer- 

 tilization. These latter are long shallow troughs divided 

 into compartments about two feet long, a foot wide and six 

 inches deep. In each compartment is a wire basket in which 



INTERIOR OF A SALMON HATCHERY 

 Courtesy of the V. 8. Bureau of Fisheries. 



are placed about 30,000 eggs. Any eggs which become 

 fungussed or otherwise diseased are removed daily to pre- 

 vent communicating the infection to other eggs. 



At first the young fish is a sack filled with yolk. Soon 

 the body appears as a narrow band extending a third or 

 half way around the sack. This little band represents mainly 

 the brain and spinal cord, back-bone and muscles of the future 

 fish. Soon the brain begins to enlarge and the eyes appear 

 as two black spots on either side, and the little fish is now 

 all head and eyes. Meantime the body is being lifted up and 

 constricted off from the yolk sack, which becomes covered 

 with a network of delicate blood vessels, connected with the 

 heart which bulges out beneath the head, for the young fish 



