DR. W. H. RANSOM ON THE OVUM OF OSSEOUS FISHES. 
483 
mometer on the stage of the microscope does not duly register the temperature of the 
eggs in the cell. 
d. Oxygen . — The experiments made with the impregnated eggs of the stickleback 
having failed to show in a satisfactory manner to what extent the contractions of the 
yelk and the cleavage are dependent upon the presence of oxygen in the surrounding 
medium, I attempted to ascertain this by employing a larger number of ova of the pike, 
which, as they exhibit the contractions of the protoplasm irrespective of impregnation, 
make it easier to separate experimentally the conditions of the cleavage from those of 
the yelk contractions ; and as they are free from any appreciable amount of maternal 
secretion, are more suitable for prosecuting the inquiry whether any and what product 
of oxidation passes into the surrounding medium, during the movements of the proto- 
plasm, or the development of the germ. 
In these experiments I divided the spinal cord of the parent fishes, without injuring 
the bodies of the vertebrae, just behind the edge of the gill-covers, and then wrapped 
them in a cloth which was kept wet, by which means they continued to live and breathe 
for some hours, and could be easily manipulated. 
Having previously prepared a curved glass tube of about in length, tapered at one 
end so as to leave an aperture of about -^- Q " to y in diameter, to which was fixed an 
elastic thread for securing it when in position, I filled the tube when warm with pure 
olive-oil and closed both ends with hot tallow, excluding air-bubbles. By this arrange- 
ment I was able to pass ova direct from the body of the parent into any fluid, without 
previous contact with air, or any air containing liquid. 
Being unable to obtain water absolutely freed from dissolved oxygen, I prepared 
several small beakers of distilled water in which were fragments of broken glass, by 
prolonged boiling, until the bumping became so violent that they were in great danger 
of being broken (indeed two or three were thus broken), and then poured pure olive- 
oil upon the water whilst boiling to a depth of f" to 1", and left them to cool. In this 
way I hoped to have water sufficiently freed from dissolved oxygen, for the purposes 
required, and in a state in which it could not support respiration. 
Thus prepared, I attempted a first series of experiments on April 5th, 1866, to ascer- 
tain whether the rhythmic contractions of the yelk persisted in water deprived, as above 
described, of its dissolved oxygen ; and at the same time whether the slower protoplas- 
mic contractions which cleave the germinal disk persisted under similar conditions. As, 
however, it was ascertained that some dissolved oxygen still existed in the water, I sought 
to obviate this difficulty by repeating the experiments with varying proportions of water 
to ova: because if oxygen be used up during these movements they must cease sooner 
when the proportion of ova to water is greater. 
I used distilled water in order that it might be afterwards tested for any product such 
as carbonic acid. 
Control experiment 1. — For the sake of having a standard of comparison, 1 put into 
a vessel of ordinary distilled water some unimpregnated eggs in the proportion of one 
