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DR DAVY’S OBSERVATIONS ON THE CHARR. 325 
seldom below 54° and never above 56°. On the 10th of December two young fish 
left their shells, and on the following day a third. They were all three feeble, as 
if their development had been premature; in a few days they died. Some eggs 
from the same fish which had been placed in Mr Reynotp’s breeding boxes were 
not hatched till the 90th day, or more than double the time. 
What the other circumstances are—other than that of mere difference of tem- 
perature—which influence the acceleration or retardation of the hatching process, 
are deserving of being investigated experimentally. Something may, perhaps, 
depend on the size and quality of the egg; something on the contact of the sper- 
matozoa, their number and activity ; and other conjectures might be offered. 
In illustration of the growth of the young fish, after quitting the egg, I shall 
briefly describe what I witnessed in the instances of three that I observed with 
some care from the time of their escape from the shell to the attainment nearly 
of their perfect form. It was on the 17th of January that they were hatched. 
Some days previously the embryos were very active, frequently changing their 
position by sudden jerks, effected by the tail and the posterior portion of the body. 
One I saw in the act of bursting the shell, now become very thin and tender. The 
rupture took place suddenly at a spot where there was a little prominence,—an 
evident yielding of the shell to the pressure from within,—and simultaneously 
the coiled-up foetus became liberated; the effort, it may be inferred, made by the 
tail, by which the opening was made, sufficing to extricate it. The instant the 
young fish entered the water, it darted about wildly for a few seconds; then 
rested, lying on its side. It was most easily disturbed ; on the slightest touch, 
even if merely applied to the water near it, it fled from the touching body, moving 
with wonderful rapidity, and in such an irregular, devious course as was well 
adapted to promote its escape from a pursuing enemy. 
These fish varied in leneth from about six-tenths to seven-tenths of an inch; 
the yolk attached was about ‘25 of an inch in length, and about ‘15 of an inch in 
depth, of an oval form. They were transparent and almost colourless, allowing 
the circulation of the blood to be seen distinctly with the microscope, using even 
a low power, such as a glass of one-inch focal distance. Their eyes appeared to 
be perfect, the lens visible and apparently prominent, the iris coloured; and, in 
accordance, the vision seemed to be acute, even the approach of a moving body, 
without coming in contact with the water, exciting alarm, indicated by a sudden 
change of place. The pectoral fins were distinct and almost constantly in action ; 
the single embryonic fin including the rounded tail, extended inferiorly to the yolk 
sac, and superiorly a little beyond the spot where the dorsal fin was to be. 
On the 30th of January, a very slight increase in their length was observable, 
about ‘02 of an inch. ‘The several fins, the dorsal, the abdominal, and anal, were 
beginning to appear in the form of slight projections from the single fin, especially 
the dorsal, in which rays were noticeable. The gill-covers now were somewhat 
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