THE PROBLEM OF MITOSIS. 
567 
The Problem, of Mitosis. 
By 
C. F. F. Heek, M.Sc., F.L.S., F.Z.S. 
Introduction. 
The first comparison of the achromatic figure and that 
representing lines of force was made in 1873 by Fol, who 
likened the centrosomes to magnetic centres ; and many 
theories of cell division have been based upon this similarity. 
Three j^eai’S later Biitschli, who with Carnoy and van Beneden 
believed that the achromatic figure is formed anew at each 
mitosis, offered a definite explanation of division founded on 
his hypothesis of the alveolar constitution of protoplasm. 
According to this explanation diffusion currents flow towards 
the centrosomes, under whose influence the entire achromatic 
figure is evolved by morphological re-arrangement of proto- 
plasm ; and the resulting increase of surface tension at the 
equator causes the cell to divide. In 1878 Klein enunciated 
the rival theory of fibrillar contractility, based upon the 
reticular hypothesis of protoplasmic structure ; he likewise 
believed that the achromatic figure is a re-arrangement of 
protoplasm under centrosome influence, but attributed the 
kinetic phenomena of division to contraction of fibrillae. This 
theory was independently suggested by van Beneden in 1883. 
Later, Niigeli attempted to explain division by an assumed 
increase of the cell periphery; and Caimoy suggested that an 
emanation of ferments from the poles is the cause of aster 
formation. 
In 1887 van Beneden elaborated the theory of fibrillar con- 
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