56 TikiUty and Organization of Protoplasm. 



intermixture of the pigmented and the non-pigmented plasm takes 

 place, but only rotation within the egg-shell; still, as different parts of 

 the egg-plasm are found to be able to exchange their ontogenetic po- 

 tentialities with regard to the evolution of the whole embryo, differ- 

 u entiation must be somehow dependent on the influence of the whole on 

 II its parts. This being the case, structural differentiations can not pos- 

 ^ sibly be preformed in the egg-plasm as specific germinal units. All 

 portions of the egg-plasm seemed here to be of equivalent potency as re- 

 gards the reproduction of the .embryo. And, of course, in this case dif- 

 ferentiation must be somehow* &ependeijt on the ijifluence of the whole 

 upon its parts. 



As these experiments of Pflueger were essentially confirmed by E. 

 and 0. Hertwig, Eoux, Driesch, Boveri and others, it is obvious that these 

 investigators were thereby logically compelled, not only to acknowledge 

 the influence of the prospective whole on its evolving parts; but they 

 were also logically compelled to relinquish the aggregational theory of 

 specifically preformed germinal units. Eoux, by confining the repro- 

 ductive substance to nuclear plasm, evaded the biological consequences 

 involved in Pflueger 's experiments. 0. Hertwig admitted that the 

 whole exerts a formative influence on its parts, but nevertheless ad- 

 hered to the opinion that differentiations of embryonic structures are 

 performed in definite particles' of egg-plasm. Driesch, on the other 

 hand, soon came fully to recognize the "^yeighty negative and positive 

 consequences involved in the equal prospective potency of different parts 

 of the egg-plasm. He repeatedly declared, that not only as regards form, 

 but also functionally is the adult organism reproduced from the egg 

 as a unitary whole. This view of the potential integrity of ontogenetic 

 evolution, whereby all its structural differentiations, and all its pro- 

 gressive stages, are subservient to the predetermined aim of reproducing 

 the whole adult organism; this view follows indeed logically from the 

 discovery of the equal "^'prospective potentiality" of different parts of the 

 egg-plasm; the potentiality here of each such part being able to repro- 

 duce the entire structure and form of the embryo. The recognition 

 of this power of fragments to reproduce the whole is, of course, of para- 

 mount importance to the science of life, as fully explained in the former 

 section. It is the real formative power in all ontogenetic evolution and 

 in all regeneration, and in fact a fundamental property of the living 

 substance. As a result of his experiments on regeneration Eugen 

 Schultz arived at the same conclusion. He says : "Eegeneration is a 

 primary property of living beings." "Upon the original capacity of 

 regeneration depends the evolution of the embryo." Biol-Centralb^att, 

 V. xxii, Jan. 15. 



The entire drift of Morgan's admirable work on "Eegeneration" tends 

 to establish the unity of the organic individual, and the subordinate 

 part cells are playing in ontogenetic evolution. His observation that 

 the diminished number of cells in fragments of the blastula has no in- 

 fluence on the power of the fragments to regenerate the entire embryo, 



