492 
DB. W. H. EAJSSOM ON THE OVUM OE OSSEOUS EISHES. 
Without, giving a detailed analysis of this group of experiments, I will briefly state 
the inferences which they appear to justify. 
The contractions of the yelk, and to a somewhat less degree, the cleavage, are remark- 
able for the small amount of oxygen which they demand for their maintenance. This 
was shown indeed in the experiments upon the eggs of the stickleback (pages 472 to 475), 
which seemed almost to justify the view that oxygen in the surrounding medium is not 
an essential condition of protoplasmic contraction, until the more extended observations 
on the pike ova enabled me to arrive at a more correct conclusion. 
The experiments a, b, c, also establish the fact, that the rhythmic contractions demand 
but little oxygen for their support, as they persisted for seventy-two to seventy-six hours 
in water deprived of oxygen, as far as it is possible to do, by boiling in air. 
The persistence of yelk-contractions in eggs which are already in part decomposing, is 
probably another illustration of this general rule. 
That cleavage also demands but little oxygen appeared from the experiments 1, 2, 3, 
on the ova of the stickleback, page 473, for it progressed in limited areas, and in water 
partly deprived of oxygen apparently as rapidly as it did in open vessels. 
One is almost led to infer, on comparing the results of the experiments upon the pike 
ova with those of the stickleback, that the former require proportionally more oxygen 
than do those of the latter during cleavage. Nor does there appear to be any difficulty 
in believing that variations in this respect exist among different species of animals. 
That some oxygen in the surrounding medium is, however, a necessary condition of 
these protoplasmic movements appears from a careful consideration of the whole of the 
observations here related, although some of the results are such as to require explana- 
tion, and no one of the experiments taken alone is entirely free from possible objections. 
I will briefly explain some of the apparently opposing results. 
In the control experiment 1, the yelk-contractions ceased in less than seventy-two 
hours, therefore earlier than they did in the ova of experiments a, b, c; this was due to 
the early setting in of decomposition in the control experiment 1, and consequent rup- 
ture and shrinking of the inner sac, phenomena which are favoured by the presence of 
oxygen in the water if it be not from time to time renewed, and were shown to be delayed 
in the boiled water covered with oil. 
But in the ova of the control experiment 2, in which the water was changed daily, 
the yelk-contractions persisted for more than 100 hours, or about thirty hours longer 
than they did in the experiments a, b , c. 
The series of suffocation experiments e to j, and e' to j' inclusive, also support the 
inference that oxygen is an essential condition ; for in all of them the yelk-contractions 
ceased long before they did in the eggs of the control experiment, and in all they 
persisted longest in those eggs which lay nearest to the accidentally admitted air- 
bubbles. 
It is true that a constant inverse relation was not observed between the numbers of 
the eggs in the cell and the duration of the yelk-contractions, but this was explained 
