^Z"V.L/uaT^^^^^^^^ of the Ovum of the Pike. 187 
also gently. Addled or dead eggs become opaque white, and should 
be always removed as soon as seen, as their decomposition will 
produce further death amongst their neighbours. The living eggs 
are of a pale yellow, and semi-transparent, having the hue and ap- 
pearance of gelatine, and apparently quite spherical. 
In about five minutes after the eggs were deposited they were 
found to cohere very strongly. A layer of them, agitated in water, 
was seen to wave up and down like a woven tissue might, without 
any break. The occurrence of this cohesion is no doubt a provi- 
sion for the secure anchorage of the eggs in their native waters ; 
they would adhere to rough stones or gravel in the same way as 
they adhere inter se. 
I may state in this place that the magnifying power I made 
use of during my observations was that afforded by a two-thirds ob- 
jective, and the low, or No. 1, eye-piece (Smith and Beck), magnify- 
ing about 72 diameters. I used this power as it was the lowest 
I had, but an inch objective will be found sufficiently high for 
such purposes. Neither is it necessary to purchase a costly micro- 
scope ; any of the cheaper microscopes of the first London makers 
will be found sufficient for those whose avocations do not demand, 
as mine did, a more expensive instrument. 
In order to watch the egg in its changes, a little circular, 
shallow glass cell, fixed by cement on to an ordinary microscopic 
glass slide, is useful. This cell must be filled brimful of water. 
To take up the egg, procure a piece of narrow gloss tubing about a 
foot long and little more than sufficiently wide in the bore to admit 
of the passage of a single egg at a time. Close one end with the 
finger, and plunge the tube into the water to a depth of 6 or 8 in. ; 
make the other end approach an egg (which must beforehand be 
gently loosened if adherent), and remove the finger which closed the 
tube ; a current of water sets in towards the interior of the tube, 
and carries the egg with it. Keplacing the finger on the end of the 
tube, the egg is retained in the tube and easily carried ofi". The lower 
end of the tube is to be moved to the surface of the water in the 
glass cell, and the egg allowed gently to sink into it, by gradually 
removing the finger from the tube. The egg and surrounding 
water are then covered by a piece of thin glass, care being taken to 
include no bubbles of air; and the whole slide is placed on the 
stage of the microscope, which stage must be fixed in a horizontal 
position. Five or six eggs may be included in the cell at the same 
time, and in this way the egg contents can be observed in several 
aspects at once. 
I will now proceed to describe what I saw by the above means. 
Unfertilized ova are found to present some of the phenomena 
hereafter described, of imbibition of water into its cavity, forming 
a water-chamber ; rotation and contraction of the yelk ; sometimes 
