88 
THE CALIFORNIAN SALMON. 
* 
The boxes being all in their places, and the water running 
well from one to the other throughout, and the screens 
fitted in their slides, the gravel may be put in them. 
It should be well washed, and, if river gravel, it 
should be boiled, so as to kill any eggs of water insects 
that it may contain. It must first be carefully screened 
to the right size, one screen taking out the larger gravel, 
and another the sand and fine gravel. "When it is 
ready it must be spread smoothly and evenly over the 
bottom, to such a depth as will leave from half an inch 
to an inch of water over it, according to the supply. The 
current should be brisk, but not strong enough to carry 
about the eggs, as rest is essential to the development of 
the embryo. When the gravel has been put in the boxes, 
they are then ready to receive the ova. If these have 
been packed in snow or ice, they should not be at once 
placed in water that may be much warmer, but the water 
should be brought down to say 40 deg. by the use of ice, 
or some other means of preventing the injurious effects 
of the shock caused by a sudden change of temperature. 
Then the ova may be distributed equally in the boxes, 
and a small stream of water turned on, to bring up the 
temperature by degrees, to that of the water in which they 
are to be hatched. It is very dangerous to expose the ova 
to dry air of a high temperature, and they should be placed 
in the hatching-boxes moss and all, and the moss can be 
easily picked out afterwards. Care must be taken not to 
keep them for any great length of time in still water, 
as it is likely to kill the embryo, and where water is 
abundant, a good current should be maintained. A 
stream of fifteen or twenty pints per minute would serve 
to hatch 50,000 ova, with an occasional shower from 
the watering-pot, and the water should be made to 
fall some distance, or be forced through a small aperture 
