INADEQUACY OF NATURAL SELECTION, ETC. 691 



Driesch, by separating the first two and the first four segmentation spheres 

 of an Echinus ovum, obtained two or four normal plutei, respectively one 

 half and a quarter of the normal size. . . . So, also, in the case of 

 Amphioxiut, Wilson obtained a normal, but proportionately diminished 

 embryo with complete nervous system from a separated sphere of a two- 

 or four- or eight celled stage. . . . Chabry obtained norrral embryos 

 in cases where some of the segmentation-spheres had been artificially de- 

 stroyed." 



These evidences, furnished by independent observers, unite in 

 showing, firstly, that all the multiplying cells of the developing 

 embryo are alike ; and, secondly, that the soma-cells of the adult 

 severally retain, in a latent form, all the powers of the original 

 embryo- cell. If these facts do not disprove absolutely Professor 

 Weismann's hypothesis, we may wonderingly ask what facts would 

 disprove it ? 



Since Hertwig holds that all the cells forming an organism of 

 any species primarily consist of the same components, I at first 

 thought that his hypothesis was identical with my own hypothesis 

 of " physiological units," or, as I would now call them, constitu- 

 tional units. It seems otherwise, however; for he thinks that 

 each cell contains " only those material particles which are bearers 

 of cell-properties," and that organs " are the functions of cell- 

 complexes." To this it may be replied that the ability to form 

 the appropriate cell-complexes, itself depends upon the constitu- 

 tional units contained in the cells. 



