DE. W. H. EANSOM ON THE OVUM OF OSSEOUS FISHES. 
475 
The slow reprotrusion of the germinal disk and commencing fusion of the masses are 
shown in Plate XVIII. tigs. 80, 81 & 82, and the ultimate flattening and fusion of the 
cleavage masses in Plate XVIII. tigs. 74 & 83. 
In order to compare the developing embryos with the developing early germs in their 
relations to oxygen in the surrounding medium, particularly with reference to the rela- 
tive need for oxygen shown by striated muscle and protoplasm during their contraction, 
I made the following additional experiments. 
Experiment 9. — One young stickleback, three days hatched, was put into a similar 
cell in tap-water and sealed ; l h 30 m after, it was quite strong, and at 4 h 30 m after, it 
could still swim about, although rather less vigorously. 
Experiment 10. — Two such young fishes were sealed in a similar cell, in some of the 
boiled distilled water before used. One of them was accidentally injured, it ceased to 
swim in a few minutes ; the gills became still first, and the heart, although it did not 
contract more than thirty minutes, last. The uninjured fish swam about for thirty 
minutes ; by forty-five minutes it had turned on its back, by l h 30 m the gills and fins 
were still ; the circulation ceased in two hours, but the heart continued for 2 h 30 m . 
Experiment 11. — The last experiment was repeated, using but one fish. In ten mi- 
nutes the gills and fins ceased to move, and the trunk to be sustained in its position, 
while in l 1 ' 10 m the heart was motionless, but the tissues were not opaque. 
Experiment 12 was the same as the last, using boiled water saturated with hydrogen, 
and taking care to choose a vigorous fish. In ten minutes the gills and fins ceased to 
move, the fish turned on its back, and after fifty-five minutes the heart alone was 
moving. 
Experiment 13 was the same as the above. In ten minutes the fish turned on its 
back, in twenty minutes the gills and fins ceased to move, in fifty-five minutes all move- 
ments had ceased, and the tissues were opalescent. 
Experiment 14 was an attempt to find chemical evidence of the presence of carbonic 
acid in the water in which eggs which had passed through the earlier stages of cleavage 
had been immersed ; but although the observation was repeated no result was obtained, 
and the details are therefore omitted. 
Although the preceding experiments were made upon such a small mass of material, 
and the methods of excluding oxygen from the surrounding medium were so imperfect, 
it may be inferred, without much risk of error, that the proportional demand for oxygen, 
of equal masses of organic matter, undergoing the changes of growth and development, 
is much less in the early germ than in the free embryo. Indeed the rhythmic proto- 
plasmic contractions and the cleavage were, to all appearance, quite unchecked by water 
deprived of most of its oxygen. The movements of striated muscle, on the other hand, 
were shown to be very soon checked in water similarly deprived of its oxygen. 
That the excess of oxygen does not hasten the cleavage, or promote or excite the 
protoplasmic contractions, appears also a legitimate inference. 
That carbonic acid acts as a potent poison is clearly shown, and that it relaxes the con- 
