The Rot in Sheep. 
Ill 
Ova. — Sufficient li;vs elsewkerc been said to sliow that the 
number of ova yielded even by one fluke exceeds any estimate 
the mind is capable of forming. Examined microscopically the 
ova are of themselves very interesting objects, apart from any 
knowledge we may have of their destination. The annexed illus- 
tration {fiy. 9) very faithfully depicts their appearance when 
Fig. 9. 
Ova of tlie^Liver-fluke, showing the manner of the escape of their contents by the 
detachment of the Opercula. Magnified. 
viewed in the field of the microscope. It not only represents 
their form, but shows the nature of their contents, and the 
manner in which these make their escape. Their size is liable 
to slight modification, some being rather larger than others. 
Many measure about liV of an inch long, and -jj-y of an inch 
broad. To the unassisted vision each egg, however, may be 
made distinctly visible, by putting a number in a small phial 
filled with water, agitating this, and then watching their fall 
while holding it to the light. Their being rendered so percep- 
tible by this procedure is doubtless due in part to their brown 
colour. 
The density of the shells of the ova is probably an important 
means for enabling them to resist decomposition, and to retain 
their vitality for a much longer period than otherwise would be 
the case. How long their vital power may continue it is im- 
possible even to conjecture. We have kept ova well covered 
with water for upwards of two years, exposed during the whole 
time to the air by leaving the cork out of the bottle, without 
observing any very great change in the larger part of them. 
Nothing at all approaching to decomposition could even then 
be detected, but whether all had retained their vitality could 
not be determined. That some, however, had done so, is evident 
from the result of the experiment. 
The experiment was begun in January, 1853, simultaneously 
with another, hereafter to be described, and was continued to 
April, 1855. On September 28, 1853, here and there an ovum 
was observed to have parted with its operculum, and a few 
circular, nucleated cells were to be detected set free in the fluid, 
of somewhat larger size, but otherwise identical with those seen 
in the interior of many of the ova. They had a tremulous 
motion, which was interrupted now and then by a jerking action 
