PHYSIOLOGICAL EFFEOTS oF Lack oF OxycEN 389 
the view I expressed a short time ago on the mechanics of 
cell-division.'. I imagine that as soon as the nucleus divides, 
vortex motions take place about each of the two daughter- 
nuclei, which leads to a tearing apart of the cell-contents; in 
other words, to cell-division.’ If this assumption is correct, 
movable particles must collect where the two vortex motions 
meet—that is, along the lines in which cleavage is to occur 
later. We indeed find this to be the case in the Ctenolabrus 
egg, and also in such eggs as carry pigment at their 
surfaces. 
These vortex motions carry the droplets to the place where 
the next cleavage is to occur, and where they are necessary 
for the formation of a membrane —a remarkable example of 
that “purposeful” interaction between mechanical conditions 
which we meet so often in processes of development. 
We see, therefore, that molecular changes—apparently a 
liquefaction and an emulsion of the membrane or the surface 
film of the cleavage-cells—occur in the case of lack of oxygen 
which gives an adequate explanation of the fact that no 
cleavage occurs in Ctenolabrus eggs without oxygen. But 
the fact that nuclear division also soon comes to a standstill 
indicates that changes corresponding to those in the mem- 
brane must also occur inside the cells. 
Vv. REVERSAL OF THE EFFECT OF LACK OF OXYGEN UPON 
ADMISSION OF AIR 
When an egg whose entire blastoderm has become invisible 
in hydrogen is again exposed to air, the changes which 
ensue differ according to the length of time during which 
the eggs have been exposed to the current of hydrogen. If 
the egg remains too long without oxygen at room tempera- 
1 Archiv fiir Entwicklungsmechanik, Vol. I. 
21 find in this case, as in that of all hypotheses, that they do not gain in attract- 
iveness with growing age. Conklin, though, has accepted the hypothesis of vortex 
motions and Butschli has justly claimed priority for it. [1903] 
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