MIDDLETHIRD HATCHING-HOUSE. 



127 



holes, and the grille was perfect. I believe I spent more thought 

 over that mode of fastening the glass tubes into the frame than 



Fia. 68 scale 



over any other individual part of the works (Fig. 69). Grilles 

 were no longer impossible for the largest piscicultund establish- 

 ments ; they were a commercial success. Fry could now be 



"^" FIG. 69 scale J. 



sold in hundreds of thousands from ova incubated on grilles at 

 less money than those hatched in any other way ; yes ; and 

 leave a larger profit ! The weight of the grille, dry, should 

 equal that of the water displaced when the grille is soaked. 

 It will then sink and rest on the supports provided ; if made 

 any heavier, the wooden frame becomes too weak, and is liable 

 to cast. The weight is only gained in making the wood pro- 

 portionally lighter than the glass, so that their combined specific 

 gravity is that of water, or a little more. The difference in the 

 vitality of fry is very great ; and as most pisciculturists purchase 

 their eggs as near hatching as possible, when they will stand a 

 very strong current, the temptation to use trays on the deep prin- 



