DYNAMICS IN EVOLUTION. 67 



figures, with their rays extending in every direction from the 

 archoplasm, with the rays developed on the surface of a fluid 

 when another fluid of definite properties is dropped upon the 

 former, leading instantly to the production of a " cohesion 

 figure" with rays extending out in every direction, is no mere 

 analogy. In the case of the archoplasm, the rays with their 

 lines of microsomes are probably the effects of diffusion of 

 one kind of plasma, the archoplasm, through another, the 

 cytoplasm, and is therefore not necessarily a phenomenon of 

 contractility, but simply an interdiffusion of the unlike sub- 

 stances produced by the metabolism of growth, which tends to 

 reestablish statical equilibrium among the parts of the molecular 

 system represented by the cell. This diffusion or osmotic 

 redistribution is conditioned at every step by surface-tension in 

 precisely the same way that the rays of many Heliozoa and 

 Radiolarians are conditioned in water by states of unequal 

 surface-tension at very close but nearly equal intervals over a 

 spherical surface, so that a summation of these uniformly 

 distributed and seemingly conflicting surface tensional forces 

 does not interfere with the maintenance of the spherical figure 

 by the body of the organism. The alternate inflation and col- 

 lapse of the nucleus during fertilization, and growth during 

 indirect cell-division, is a rhythmical process, and we may char- 

 acterize it as the diastole and systole of the nucleus. The alter- 

 nate extension and retraction of the rays of the archoplasm, as 

 I have observed in the egg of Ascaris, is similarly an osmotic or 

 metabolic diastole and systole of the radial figures formed by it, 

 which is intimately associated with and absolutely conditioned 

 by metabolism and osmosis, as the direct experimental researches 

 of Prof. Jacques Loeb have rendered exceedingly probable. 

 Unless the processes of karyokinesis are traced with the 

 utmost caution in the light of dynamical and physiological 

 considerations, there is great clanger of our misinterpreting the 

 facts and of assuming that certain of the phenomena guide 

 and control others. It may indeed be possible that embryolo- 

 gists have been until now steadily confounding ontogenetic 

 effects due to the physical processes of growth, as visualized 

 in karyokinesis, with their causes. I anticipate that this 



