A DYNAMICAL HYPOTHESIS OF INHERITANCE. 45 



have been most exhaustively studied by Professor E. G. ConkHn, 

 regulate segmentation, still remains to be determined. There 

 can, however, be but one explanation of such movements, and 

 that must be a mechanical one, but its nature is entirely 

 unknown. Wilson has shown that the conditions of free and 

 interfacial surface-tension in Amphioxus vary in different eggs 

 from some unexplained cause, so that the earlier cleavages of 

 this form also vary to a corresponding and remarkable degree. 

 In other cases surface-tensional forces operate under similar 

 recurring conditions. In the fish-egg I have witnessed the 

 reappearance of the same or similar interplay of statical 

 energies thrice in succession, so as to produce three similar 

 successive sets of formal changes in the egg that are traceable 

 to the action of similar statical agencies. In A, Fig. 4, the 



Fig. 4. 



germ a has assumed a lenticular form of statical equilibrium ; 

 after segmentation of the same disk has proceeded some way, as 

 in B, the disk, as a cellular aggregate, has again assumed the 

 lenticular form of equilibrium, while the outermost row of cells, 

 c, are individually in a similar condition of equilibrium. 



These facts are quite sufficient to estabhsh the general truth 

 of the statement that at no stage is the ontogeny of a species 

 exempt from the modifying effect of the surface-tensions of 

 its own plasma acting between the cells as if they were so 

 much viscous dead matter. Such statical effects are not over- 

 come at any stage of the development, or even during the life 

 of any organism. On account of the universal presence and 



