180 Flow to obtain it. 
removal they were placed on fresh grilles, whilst the others were 
being dried and re-varnished, ready for further use. Apart from 
‘accidental scratches, which let in the water, it will percolate through 
and corrode the metal, and wherever this corrosion takes place the 
eggs suffer. One very weak point I have found to be the place 
where the wires enter the wooden frame. At this point it is 
often difficult to prevent corrosion taking place during the period 
of incubation, and wherever it does take place, there it causes 
injury to the delicate embryos. It may not kill them at once, 
but it weakens them so that they cannot live to grow up. 
Livingstone Stone says :—“ Fourteen trout eggs were placed 
on a copper-wire screen in November, 1869, at the Cold Spring 
Trout Ponds, and in fifty days they had absorbed so much copper 
that they were of a dark brown tinge and hard like peas.” Many 
of my correspondents have found metallic trays, chiefly zinc, very 
hurtful indeed to the ova. 
It is better to work with fewer eggs, and to do the work well, 
than to go in for large numbers ; and I would hand on this piece 
of advice to all who contemplate having anything to do with the 
incubation of ova. It is the key to the whole work, and any point 
overlooked, however trivial it may appear at the time, may cause 
wreck and ruin afterwards. The preparation and incubation of 
the ova is a special work, requiring much care and attention, and 
can only be successfully done by those who thoroughly understand 
it. The hatching of ova, after having been properly prepared and 
incubated, is a very simple matter indeed, and can be done by 
any man of ordinary intelligence. So simple and easy has it been 
made, indeed, that the eggs, as already explained, will hatch them- 
selves, if placed in a well-made artificial hatching bed. It is here 
that we gain considerably on Nature. Nearly all the loss which 
takes place in the egg stage is prevented. 
Loss has been variously estimated by different specialists, but 
we are not far from the mark in assuming that a very small per- 
centage, indeed, of the eggs naturally deposited in our streams live to 
produce mature fish. The number probably varies a good deal 
according to circumstances, but we know that in many cases not 
one egg in a thousand survives. Whole spawning beds are some- 
times washed away, and the contents destroyed. The host of 
