468 AMERICAN ANGLER'S BOOK. 



These, as the reader will observe from the cut, are simply 

 a succession of troughs placed one above the other. The 

 water flowing from the stop-cock B, in any desired quantity, 

 into the topmost trough, falls in little cascades into those 

 below, which aerates it sufficiently during the term of hatch- 

 ing. By means of these troughs the fecundated eggs may be 

 watched with care, and examined without the danger of dis- 

 turbing the process of incubation, as would be the case if 

 the spawn was placed in hatching-boxes, according to M. 

 Grehin's plan, and deposited in the stream, and removed from 

 it occasionally to examine them. 



The troughs may be placed in any spare room where it is 

 convenient to lead a small supply -pipe, and place another for 

 the discharge of the water. They should be supplied to the 

 depth of four inches with clean gravel and a little coarse 

 sand. Each trough should be raised somewhat at the end 

 where it receives the overflow from the trough above, so as 

 to cause a slight current. M. Coste recommends that the eggs 

 be spread on closely- woven hurdles of willow, and sunk an 

 inch or two below the surface ; his reasons for doing so are 

 given in a subsequent extract. If the bottoms of the troughs 

 are covered with gravel, the water which may be supplied 

 through a quarter-inch pipe should flow through them for 

 a few days, so as to remove any impurity amongst the peb- 

 bles. 



