PHYSIOLOGICAL EFFEcts oF Lack oF Oxygen 401 
If the eggs have divided into two or four cells, and the 
oxygen is then removed completely from them, the cell-limits 
become indistinct in about three hours. The cells then 
absorb water in consequence of the effects of lack of oxygen. 
The volume of the eggs increases, and the space within the 
membrane is soon filled uniformly with the protoplasm of 
the cleavage-cells. The outlines of the cell then become 
invisible, and the egg looks as if it had never divided. If 
oxygen is readmitted, the eggs cleave anew, if too long a 
time is not allowed to elapse. In many cases the old lines 
of cleavage reappear, but this is by no means always the case. 
The changes remind one of those in the eggs of Ctenola- 
brus, only that they occur more rapidly and more distinctly 
in the latter than in the eggs of the sea-urchin. 
The surface of the cleavage-cells of the Arbacia is pig- 
mented, and the pigment granules move upon the surface of 
the egg during cleavage. I do not doubt that by more care- 
ful study phenomena similar to those observed in the cleavage 
of the Ctenolabrus and the Fundulus eggs will be observed 
in the case of Arbacia also. 
The fact has been mentioned that, in general, the cleavage 
of the Fundulus egg without oxygen occurs not only just as 
rapidly as under normal conditions, but even a little more 
rapidly, as stated in my paper on “The Relative Sensitiveness 
of the Fundulus Embryos in the Different Stages of Devel- 
opment against Lack of Oxygen.” In that article, however, 
I attributed this difference in time to the increase in tempera- 
ture brought about in sealing up the test-tubes used in the 
experiments. Since I again noticed these changes this year, 
first in the Ctenolabrus egg, and later in the Arbacia egg, 
in an Engelmann chamber—where there was, therefore, no 
considerable increase in heat——I decided to determine by 
more careful experiments whether this difference in time is 
indeed dependent entirely upon differences in temperature, 
Digitized by Microsoft® 
