THE CALIFORNIAN SALMON. 
87 
four feet above the ground, for convenience in picking out 
the dead eggs, and for examination of the fish and eggs 
from time to time. The stone race being on the level of the 
ground necessitates the kneeling posture in examining 
them, which becomes very irksome and inconvenient, as the 
young fish cannot be seen so well, and dead ones may be 
left in the race, thereby fouling the water, to the injury of 
the live fish. 
The hatching-boxes were each secured at the ends with 
fine screens of perforated tin. These must be smaller in 
the perforations than the finest perforated zinc that I 
could obtain, which I found would let young fish go 
through. I first tried woven screens of copper wire, 
but finding the deaths amongst the ova to increase rapidly, 
I suspected that something was wrong, and had tin ones 
inserted instead. I found that I had unwittingly, by the 
combination of zinc and copper, constructed a galvanic 
battery, which, no doubt, was destroying the ova. I found 
that M . Coste had on one occasion made the same mistake, 
which he described in a paper sent to the Societe Imperiale 
d' Acclimatation, and which suggested this as the possible 
cause of the loss which had occurred. The boxes were 
also divided by a screen into two parts, to prevent 
the young fish from crowding to the end where the water 
enters, which they are eager to do. 
The boxes must be kept carefully covered, so that not a 
crevice may be left where a mouse, snake, or lizard could 
enter, as they would make short work of either ova or 
alevins — as the newly-hatched fish, until the umbilical 
sac is absorbed, are called — once they gained access to 
them. A portion of the cover should be of perforated 
zinc, to admit light, which, although not needed during 
the process of hatching, is essential to the health of the 
young fish when hatched. 
