THE CALIFORNIAN SALMON. 
81 
when any deposit becomes visible. The slime is injurious 
in preventing the proper supply of oxygen, required by the 
egg to vivify the embryo, from reaching it, and if the 
deposit be allowed to remain long on the ovum, it causes 
certain death to the embryo. The temperature of the 
water is an important point, and the coolest water is to be 
preferred, as fish hatched in cold water are said to be more 
robust, than those hatched at higher temperatures. A good 
spring, if not impregnated with any injurious mineral sub- 
stance, is the best, as the temperature varies little, and the 
water is generally free from sediment. Any good water 
will do, however, even if muddy, provided some pure water 
can be used occasionally, to enable the attendant to see the 
ova, and by the very frequent use of the watering-pot to 
wash off the sediment. I have known trout ova hatched 
out very successfully by Mr. Richmond, at Learmonth, in 
water raised by a windmill from the lake, which was so 
muddy, that neither ova nor fish could be seen in it, 
until a few buckets of rain water were poured into the 
hatching boxes — which was done daily to make the ova or 
fish visible so that dead eggs or fish might be removed. 
These ova were within a few days of hatching, however, 
when placed there. 
I will now describe the hatching boxes, which I have used 
with success, and which are very convenient, and in every 
way suitable. They are about six feet long by two broad, 
and six inches deep. They are made of three-quarter-inch 
pine-boards, and are covered outside with zinc with the joints 
soldered, so as to be water-tight. At the end is an overflow 
spout made of zinc, a foot in width, which conducts the water 
from one box to the other, and which, by being spread out 
in a thin sheet, gets aerated by being brought into contact 
with the atmospheric air. On the bottom of these boxes 
two or three inches of gravel is placed, so that the water 
