PRESIDENTS ADDRESS. 20 



material system the germ must necessarily possess, registered 

 either in its phj'sical structure, or in its chemical composition, or 

 in both together, potential equivalents of those properties in 

 which it resembles the parental organisation. To deny the 

 existence of .some such physico-chemical embodiment seems to me 

 tantamount to asserting, not only that the properties of a germ 

 are not those of a purely material sytem, but that the entire 

 phenomena of reproduction are essentially unintelligible. 



To admit so much is of course a very different thing from 

 admitting the whole contention of the thorough-going preforma- 

 tionists. It amounts to no more than the assertion of a structural 

 basis for organisation, not only in the ovum but in the 

 developing organism itself. " Continuity of organisation," says 

 Whitman, " does not of course mean preformed organs, it means 

 only that a definite structural foundation must be taken as the 

 starting-point of each organism," whose " organic unity must 

 depend on intrinsic properties no less than does molecular unity." 

 "The indubitable fact on which we now build is no bit of 

 inorganic homogeneity, but the ready-formed, living germ, witli 

 an organisation cut directly from a pre-existing, parental organisa- 

 tion of the same kind. The essential thing is not simph- 

 continuity of germ-suljstance of the same chemico-physical con- 

 stitution, but actual identity^ of germ-organisation with stirjv 

 organisation." 



The facts of regeneration are confidently appealed to in order 

 to support the contention that the differentiation of structure in an 

 organism is governed by a general morphological idea of organic 

 unity, and not by any sort of mechanical predetermination of its 

 structural parts. And one may frankly admit the entire inability 

 of conceiving how, by some physical arrangement of determinants, 

 the half-embryo which results from the development i7i situ of one 

 only of the first two blastomeres, should possess the capacity of 

 regenerating the other half. Yet we are not entitled to adopt 

 the extreme views formerly expressed by Driesch, which assume 

 the absolute isodynamy of the early embryonic cells, according to 

 which theory they may be " thrown about at will, like balls in a 



