SALMON. 
183 
England, a much shorter time will be sulEcient for the 
purpose. It is known accordingly that the roe of this fish 
has been developed into lile in these last-named districts 
within the space of sixty days; and in proof of this hastening 
influence of temperature Dr. Knox procured grains of roe 
which had lain in the sand for a hundred and sixteen days, 
but had not yet shown signs of becoming hatched; yet when 
these were placed in a bottle, with their native water, and 
brought into a warm room, the actions of life vei’y soon 
displayed themselves. It is to be observed, however, that 
when thus hastened on, and the regular course artificially 
interfered with by a sudden application of heat, or too high 
a degree of it, the very young fry are much less likely to 
survive it. Dr. Davy found a temperature above seventy 
degrees, and up to eighty, to be certainly fatal to the eggs 
of fishes of this family, as also of some other fishes. In Mr. 
Shaw’s experiments on the breeding of Salmon, when the 
temperature of the stream he employed was at thirty-nine 
degrees, and of the main river from which the breeding 
Salmon were taken thirty-three, with that of the atmosphere 
thirty-six, the embryo after fifty days was seen to be able to 
move under its covering; and it escaped from the egg when 
the temperature was at forty-four: but the whole of this 
implies a far deeper degree of cold than is the average of 
rivers at the same season in the south-west of England. Mr. 
Shaw remarks that the ^^ova which for a time previous to 
being hatched had been almost daily in my hands for inspection, 
did not appear to suffer at all from being handled. When I 
had occasion to inspect the ovum I placed it in the hollow 
of my hand, covered with a few drops of water, where it 
fiecjuently remained a considerable time without suffering any 
apparent injury.” But afterwards he admits that it shewed 
an increase of activity from the heat of his hand, and the 
variation of temperature thus produced would probably lead 
to injuiious consequence, although the young at last seemed 
capable of surviving longer than Dr. Knox supposed. This 
last-named gentleman found sometimes that they had quitted 
the gravel by the 1st. of April, but at other times it was not 
for upwards of a fortnight after this; while on another occa- 
sion Sir Francis Mackenzie made the experiment, on the 
