THE AETIFICIAL INCUBATION OF OVA. 33 



and run out witli the water, and, if needful, the tray- 

 scrubbed, the cork replaced, and the tray refilled, per- 

 fectly clean and purified. By keeping a spare tray at 

 the foot of any range of trays, and simply shifting the 

 grilles tray by tray, the whole range of trays may thus 

 be cleaned thoroughly without risk of danger to the 

 ova, particularly after the eye becomes visible in the 

 egg.^ "When the embryo hatches out of the egg it 

 falls between the bars to the bottom of the tray, 

 and as soon as a good number of them are collected, 

 the unhatched eggs can be shifted on the grille to 

 another tray ^o tern., and the alevins drawn off 

 through the hole (a) into a suitable vessel held to 

 receive them, and deposited in a proper rearing 

 tray. These French trays^ as they are at present 

 constructed, are bad rearing trays, however. In the 

 first place, they are too deep. Alevins and fry 

 require more stream than they get, and to this end 

 two inches depth of water is ample. Three inches 

 or three and a half inches is too much; for it 

 does not allow of a sufi&ciently rapid change of 

 the water, as the runniug water goes off on the 

 surface without touching the lower depths, conse- 



1 I may remark here, that wntU the eye is developed in the egg 

 these shiftiDgB should be as sddom as possible, as perfect rest is very 

 advantageous to the egg.— F. F. 



D 



