50 BIOLOGICAL LECTURES. 



which is to be attained in future. This is the idea that under- 

 lies the Vervollkommmings-P rincip , principle of perfecting, of 

 Nageli. This view also tacitly recognizes the theory of change 

 of function proposed by Dohrn, as well as the theories of sub- 

 stitution, superposition, and epimorphosis of Kleinenberg, 

 Spencer, and Haacke. Once a condition of stable equilibrium 

 has been reached in the series of transformation of the molec- 

 ular mechanism represented by the germ, during the develop- 

 ment of an organism, we may have what Eimer has called 

 Genepistasis, resulting in the fixity or stability of an organic 

 species, under stable conditions. 



The cell is a complete organism, but it loses its physiological 

 and morphological autonomy when combined with other cells. 

 We may regard the nucleus, cytoplasm, and centrosome as re- 

 ciprocally related parts ; one of them not much more important 

 than the others. The observed behavior of the centrosome 

 would indicate, as Verworn has held, that it is the important 

 agent in cellular metabolism. If this is true, metabolism has 

 certain centers in the cell to and from which molecular trans- 

 formations are effected rhythmically in every direction, with 

 the centrosomes as focal points. This view agrees perfectly 

 with the facts, since the rays of the asters may be regarded as 

 the morphological expression of a dynamical process of inter- 

 molecular diffusion due to metabolism, as Kolliker has sus- 

 pected {Geivebelehre, 6th ed.). 



Such a process would not only serve to alter the surface and 

 interfacial-tensions of the cells during ontogeny, but also vary 

 the osmotic pressure within them. Consequently, we may 

 conceive that all of the phenomena of development, including 

 the appearance and disappearance of cavities within a germ by 

 changing conditions of osmosis, may receive a dynamical expla- 

 nation. The centrosomes may, moreover, be conceived to lie at 

 the foci of very complex material figures, the boundaries of which 

 are finite equipotential cellular surfaces. These focal points are 

 clearly near or within the nuclei. The equipotential surfaces 

 developed by the sorting or readjusting process that goes on 

 during segmentation in order continually and rhythmically to 

 restore the dynamical equilibrium of the molecular germinal 



