IV] AND STRUCTURE OF THE CELL 309 



dividing centrosome, while moving apart, take some twenty minutes 

 to travel a distance of 20 /x, or at the rate, say, of two years to a 

 yard. It is a question of inertia, and the inertia of the system must 

 be very large. 



The beautiful technique of cell-culture in vitro has of late years 

 let this whole succession of phenomena, once only to be deduced 

 from sections, be easily followed as it proceeds within the living 

 tissue or cell. The vivid accounts which have been given of this 

 spectacle add little to the older account as we have related it: 

 save that, when the equatorial constriction begins and the halves 

 of the split chromosomes drift apart, the protoplasm begins to show 

 a curious and even violent activity. The cytoplasm is thrust in 

 and out in bulging pustules or "balloons"; and the granules and 

 fat-globules stream in and out as the pustules rise and fall away. 

 At length the turmoil dies down; and now each half of the cell 

 (not an ovum but a tissue-cell or "fibroplast") pushes out large 

 pseudopodia, flattens into an amoeboid phase, the connecting thread 

 of protoplasm snaps in the divided cell, and the daughter-cells fall 

 apart and crawl away. The two groups of chromosomes, on reaching 

 the poles of the spindle, turn into bunches of short thick rods; these 

 grow diffuse, and form a network of chromatin within a nucleus; 

 and at last the chromosomes, having lost their identity, disappear 

 entirely, and two or more nucleoH are all that is to be seen within 

 the cell. 



The whole, or very nearly the whole, of these nuclear phenomena 

 may be brought into relation with some such polarisation of forces 

 in the cell as a whole as is indicated by the "spindle" and "asters" 

 of which we have already spoken: certain particular phenomena, 

 directly attributable to surface-tension and diffusion, taking place 

 in more or less obvious and inevitable dependence upon the polar 

 system. At the same time, in attempting to explain the phenomena, 

 we cannot say too clearly, or too often, that all that we are meanwhile 

 justified in doing is to try to shew that such and such actions He 

 within the range of known physical actions and phenomena, or that 

 known physical phenomena produce effects similar to them. We 

 feel that the whole phenomenon is iiot sui generis, but is some- 

 how or other capable of being referred to dynamical laws, and to 



