iv] NATURE OF THE SPINDLE 49 



Some have maintained that the force in question is actually 

 electric; others, for example, HARTOG, regard it as a force 

 peculiar to the living cell. 



In the space available only a very brief statement of the 

 arguments for and against each of these hypotheses can be 

 given. Most of those who accept the view that all proto- 

 plasm has a reticular or alveolar structure also hold that 

 the mitotic spindle consists of a local rearrangement of the 

 fibres or alveoli, giving rise to the spindle and astral fibres, 

 and this opinion has also been supported by some who do 

 not take any decided view on the structure of protoplasm 

 in general. For example JzNKiNSON,in the work on the egg 

 of the Axolotl already referred to, concluded that the asters 

 and spindle were due to alveoli radiating from centres into 

 which fluid was attracted owing to their osmotic condition. 

 According to him, the asters in this case consist of radiating 

 alveoli surrounded by a zone of finer rays which are due to 

 the path of the fluid travelling towards the centres; the 

 spindle is formed by the meeting of elongated alveoli from 

 the two centres, in such a way that continuous tubes are 

 formed from one centre to the other, and the fibres are 

 produced by the partial coalescence of neighbouring tubes, 

 the walls of which give rise to viscous threads. These 

 threads become attached to the chromosomes, and when the 

 chromosomes divide, the halves are drawn towards the 

 centres or poles of the spindle by the contractility of the 

 viscid threads. Many other investigators have given some- 

 what similar accounts of the origin and mechanism of the 

 spindle, differing indeed in detail, but agreeing in the 

 essential features that the spindle consists of the same 

 substance as the rest of the cytoplasm, and that the fibres 

 draw the divided chromosomes towards the poles by their 

 own contractility. This is essentially the view associated 

 D.C. 4 



