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 7J 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 6f in. long and 5 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 {i>) 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 (c) prevents any egg lapping over 

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

 fry when the eggs hatch out. 



