INADEQUACY OF NATUBAL SELECTION, ETC. G91 



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

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

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

 uS Wil 



ilson 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. 



