SURFACE TENSION AND CELL-DIVISION 



245 



It is somewhat rash, perhaps, to press too far the analogy 

 of the astral figure to the rings in Plateau's experiment. It 

 is obvious that the mechanical model is a limited one, and that 

 subsequent work may show that regions of differential viscosity 

 such as are suggested by Chambers's ^ work may be found 

 to be involved. Yet in the particular case of a cell which 

 possesses a structure curiously fitted to play the part of 

 Plateau's rings, division is found to proceed on just those lines 

 demanded by the above analysis. Text-fig. 9 shows the division 



Text-fio. 9. 



Protoplasm 



Division of C o 1 e p s h i r t u s (after Doflein). The undivided form a 

 gives rise to two daughter individuals by passing through stage B. 



I 



of the protozoon Coleps hirtus. The body is covered by 

 four hard skeletal plates P1-P4. When division occurs the 

 distal ends of the cell remain fixed in form owing to the existing 

 plates, and between plates P., and P4 the cell becomes elongated 

 in exactly the form demanded by the hypothesis put forward. 

 In the stage of division illustrated a well-marked cleavage 

 furrow has formed and the ' Plateau ' ratio is about -8. 



Summary. 



Cell-division may be accounted for by the movement of the 

 two asters away from each other. The appearance of the 

 cleavage furrow is due to an equilibrium between the effect 

 of this movement on the protoplasm and the surface tension 

 at the cell-surface. The behaviour of the cell under these forces 

 is precisely similar to a drop of oil subjected to similar condi- 

 tions. There is no necessity to postulate regions of differential 

 surface tension at the poles or equator of the cell. 

 1 ' Journ. Exp. Zool.', vol. 23, p. 483, 1917. 



NO. 262 S 



