OUR RIVER HARVESTS. 275 



these cups, and each is intended to hold one egg, so 

 that the tedious process of counting the ova is no longer 

 required. 



When the eggs are properly arranged the water is 

 permitted to flow very gently over them, and its force 

 is gradually increased until it imitates as nearly as 

 possible the shallow rippling part of the stream where 

 the fish generally lays its eggs, and the motion of which 

 seems to be essential to the hatching of the egg. The 

 stream is about one inch in depth. 



One great advantage of this plan is that the eggs 

 and young are always kept in view, and are at a con- 

 venient height from the ground, so that they can be 

 watched with a lens through the crystalline water, and 

 their changes noted from day to day. 



Another establishment is placed in the open air, not 

 very far from the banks of the Thames. This consists 

 of a series of flat troughs made of elm, and measuring 

 four feet in length, fifteen inches in width, and eight in 

 depth. These troughs or boxes are furnished with 

 gravel and stones, as has already been mentioned ; they 

 are set end to end, and water flows continually through 

 them from a little spring which has been ingeniously 

 diverted in the proper direction. 



The eggs are placed in the upper boxes, covered 

 with coarse gravel, and the water suffered to flow 

 gently over them until they are hatched, an event 

 which usually takes place in sixty or seventy days. The 

 temperature of the ' water has, however, much to do 



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