24 
DR. DAVY ON THE OVA OF THE SALMON, 
average than those constantly kept in water. These ova were from the Leven. In 
another experiment, with ova last received from the Dee, four were kept in a vial of 
the same capacity and merely moist within, fourteen days without apparently suffer- 
ing ; they were all hatched on being replaced in water. And, in a third trial, two 
ova, also from the Dee, have been kept in moist wool twelve days, also without any 
appearance of injury, these too having been hatched after having been put into water. 
in. Of Exposure in Air and TVater to a Temperature at or below the Freezing-^point. 
1. An ovum exposed on a watch-glass to the open air from 4 p.m. one day to 10 a.m. 
the following, the thermometer at 30° at the commencement and termination of the 
trial, had become slightly shriveled and its circulation was stopped; put into water 
with snow, so as to be gradually thawed if frozen, it did not revive ; its death was 
denoted by its yelk becoming opake. 
2. An ovum exposed to the open air at about 30° for an hour, was found adhering 
to the slip of glass on which it rested by a frozen drop of water, so that it could be 
carried inverted without falling off. Under the microscope, still attached to the glass 
by ice, the blood-corpuscles were seen in slow motion in the vessels ; in one vessel 
they were moving backward and forward. Where adhering to the glass the ovum 
was slightly flattened. Removed to water, the following day the embryo was seen 
active and the circulation vigorous ; thirteen days later the young fish burst its shell, 
and was to all appearance uninjured. 
3. Another ovum, exposed to the open air of 29° for an hour and twenty minutes, 
was found frozen to the glass, but without loss of vitality. The result was the same 
as. that of the preceding experiment. 
4. An ovum exposed in water in a watch-glass to the open air during the night, 
tlie thermometer so low as 20°, was found in the morning included in ice and dead ; 
the yelk had become opake and was probably frozen. 
h. Exposed an egg in a wine-glass to the open air from 3 p.m. one day to 10 a.m. 
the next, the thermometer as low as 22°. The whole of the water was frozen ; when 
thawed no circulation was visible in the ovum; two days after a feeble circulation 
was detected, which ceased the following day and the yelk became opake. 
6. An ovum exposed in water to the open air, about 31°, in an hour was covered 
with a pellicle of ice ; the circulation had become languid. An hour and a half later, 
the thermometer at 30°, the ovum was included in ice ; the circulation much the 
same. Tiie experiment was continued about eighteen hours longer, the ovum in- 
cluded in ice at about the same temperature ; the circulation was now languid but 
distinct, and the ovum was nowise altered in appearance. 
7- An ovum was exposed in water in a wine-glass to the open air below the freezing- 
point. When a pellicle of ice had formed on the water, the glass was surrounded 
with wool in a little box and left in the open air. During the night the thermo- 
meter fell to 9°. The ovum in the morning was found adhering to the bottom of the 
