PHYSIOLOGICAL EFFECTS OF LACK OF OXYGEN 389 



the view I expressed a short time ago on the mechanics of 

 cell-division. 1 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. 2 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. 



V. EEVERSAL 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 fur Entwicklungsmechanik, Vol. I. 



2 1 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] 



