324 



ON THE INTERNAL FORM 



[CH. 



convergent curves of the spindle, are replaced in the later phases of 

 caryokinesis by divergent curves, indicating that the two foci, which 

 are marked out in the field by the divided and reconstituted nuclei, 

 are now ahke in their polarity* (Figs. 100, 101). 



The foregoing account is based on the provisional assumption 

 that the phenomena of caryokinesis are analogous to those of a 

 bipolar electrical field — a comparison which seems to offer a helpful 

 and instructive series of analogies. But there are other forces which 

 lead to similar configurations. For instance, some of Leduc's 

 diffusion-experiments offer very remarkable analogies to the dia- 

 grammatic phenomena of caryokinesis, as shewn in Fig. 102 f. 



Fig. 102. Artificial caryokinesis (after Leduc), for comparison with Fig. 88, p. 299. 



Here we have two identical (not opposite) poles of osmotic con- 

 centration, formed by placing a drop of Indian ink in salt water, 

 and then on either side of this central drop, a hypertonic drop of 

 salt solution more lightly coloured. On either side the pigment of 

 the central drop has been drawn towards the focus nearest to it; 

 but in the middle line, the pigment is drawn in opposite directions 

 by equal forces, and so tends to remain undisturbed, in the form of 

 an "equatorial plate." 



To account for the same mitotic phenomena an elegant hypothesis 

 has been put forward by A. B. Lamb J, and developed by Graham 



* W. R. Coe, Maturation and fertilisation of the egg of Cerebratulus, Zool. 

 Jahrbiicher {Anat. Abth.), xii, pp, 425^76, 1899. 



t Op. cit. pp. 110 and 91. 



t A. B. Lamb, A new explanation of the mechanism of mitosis, Journ. Exp. Zool. 

 V, pp. 27-33. 1908. 



