MARINE PISCICULTURE 309 



The fertilised eggs, by whatever method they 

 are obtained, are cleaned by washing in pure sea- 

 water, and they are then put into the " hatching- 

 boxes." These apparatus are generally small boxes 

 about a foot square, open at the top, and having a 

 bottom made of a fine but strong sieve of horse- 

 hair. They are arranged in sets, and float in 

 connected compartments in a large wooden tank, 

 also filled with water. Water enters into each 

 hatching-box at the top, and passes out through 

 the sieve forming the bottom. By an automatic 

 arrangement of some kind or other the hatching- 

 boxes are jerked up and down at regular intervals, 

 and in this way the eggs, which normally float at 

 the surface of the water, are kept from collecting 

 there as a layer, and receive sufficient aeration by 

 the motion of water caused by the jerking of the 

 boxes. The sea-water which is made to circulate 

 through the hatching-boxes is selected for its 

 freedom from sediment and its high specific 

 gravity. If there should be much sediment in the 

 water, this is apt to settle down on the eggs, and so 

 impede their oxygenation. If the specific gravity 

 is low, then the eggs may sink to the bottom. It 

 is often necessary to filter the water used in the 

 hatching-boxes, though a high degree of freedom 

 from sediment is not so essential as is often 

 supposed. 



The average volume of the eggs dealt with is 

 known, so that, by measuring the total bulk put 



