1 84 THE SEA-TROUT 



been called the "American " system. But meantime, to get rid of 

 structural details, it will be sufficient now to describe one of the hatching 

 boxes, arranged for the glass grille system (see box marked V on plan), 

 and one fitted with the perforated zinc baskets (see box marked XI on 

 plan). The glass grille system is the more effective for hatching out 

 ova. It shows a slightly lower percentage of loss than the basket 

 system, but its practical drawback is that it requires more space in 

 proportion to the number of ova dealt with. 



The hatching boxes (and the boxes for each system are so far 



identical) are made of i^ in. dressed deal carefully charred inside. 



Each is 6 ft. 9 in. in length, i ft. 7 in. broad, and 7| in. deep, outside 



measurements (see box marked I on plan). The box has wooden 



ledges on each side of the bottom, and a removable wooden runner in 



the centre placed longitudinally (see box marked II on plan). On 



these rest the four frames A, B, C, D, carrying the glass grilles (see 



box marked IV on plan). The grille upon which the ova rest is a series 



of glass tubes, each tube being 6| in. long and J in. in diameter. The 



tubes are set in a row close together, but not touching, across each 



frame (see frame marked E in box marked V on plan), and are kept in 



position by serrated wood or zinc strips fixed to the inside edges of the 



frame. The level of the frames in the box is so adjusted that the eggs 



when placed upon the grille are 3 in. from the bottom of the box, giving 



that depth of water beneath them, while the water-level is maintained 



at half-an-inch over them. As it is important to strain the water of all 



sediment, the nose-cock at the upper end of the box discharges first 



into a perforated zinc strainer (a) which, with a further inch or two of 



space (/') before the trays are reached, distributes the inrush of water 



to the box in a uniform gentle flow. At the lower end of the box a 



removable perforated zinc screen (r) prevents any egg lapping over 



into the lower box, and, later, prevents the escape of the alevins and 



fry when the eggs hatch out. 



