214 THE MICROSCOPICAL NEWS. 
catch such fish as may have found their way out of the’ in- 
cubator. 
Later on, when all the fry have hatched out and the empty egg- 
shells disappeared, the escape of the young fry is prevented, and 
their safe confinement to the incubator ensured, by suspending a 
smaller wire-bottomed tray d in the larger ditto ¢ just before the 
entrance to the spout. 
Concerning the quantity of eggs to be placed in the tray, and 
afterwards of alevins to be kept in it, experience has shown that in 
the case of trout and salmon ova and fry, when the temperature of 
the water is 32° Fahr., 10,000 is not too large a number ; whereas 
if the temperature is as high as 50° Fahr., the number should not 
exceed 5,000, 
As the current flows right through the eggs, they sustain no 
injury from being piled up several layers in thickness. The 
culturist should, however, avoid touching or moving them as 
much as possible during the earlier portion of the incubating 
period ; for until they have reached the “eyed” stage of develop- 
ment they are exceedingly sensitive and easily killed. 
Whilst until then the removal of the dead and diseased eggs 
demands great care there is no danger connected with the 
operation, or with that of clearing away sediment from the time of 
the appearance of the eye-spots, and this absence of danger greatly 
facilitates the work. 
After the defective eggs on the surface have been picked out 
with a pair of nippers the culturist takes hold of that end of the 
large tray which is furthest from the spout, gently tilts it up, and 
then quickly sets it down again. ; 
Each time this operation is repeated, the rising current causes 
the eggs on their descent to be differently distributed, and there is 
thus little chance of any worthless ones escaping notice. 
Should any sediment collect on the ova, it is cleared away by 
sprinkling them well with a watering can furnished with a finely 
perforated rose. Before this can be done, the water in the incu- 
bator must of course be drawn off, the syphon generally used for 
the purpose consisting of an India rubber tube, which is hung over 
the side of the outer division 4 of the hatching trough, and reaches 
to the bottom of the apparatus. 
When possible, the cleansing process should be deferred till the 
eggs are eyed. 
Another precaution the culturist should observe is not to raise 
the large tray ¢ of the incubator until the salmon and trout alevins 
have partially absorbed their umbilical sacs. 
In the case of the fish just named the yolk-sacs are at first very 
large, and if the tray were then by mischance lifted at all quickly 
they might be pressed by the strong current through the wire-netting. 
