REGENERATION 185 



pierced with a hot needle one of the two cells 

 formed by the ovum of the frog as the result 

 of its first division. If the experiment was 

 successfully carried out, the ovum did not 

 perish, but the uninjured cell went on with its 

 development with the result that a half-embryo 

 was formed. A little thought will show that 

 this experiment seemed to be a proof of pre- 

 formation, for it could be argued from it that 

 the very first division of the ovum divided the 

 developing individual into its two lateral 

 halves. So matters remained until 1891, when 

 Driesch repeated Roux's experiments on the 

 egg of the common sea-urchin. Here diametric- 

 ally opposite results were obtained, for instead 

 of the half-embryo, a complete but small em- 

 bryo resulted. Moreover, even in the next or 

 four-cell stage, two or three of the cells could 

 be destroyed yet a small but still perfect 

 embryo resulted. Further, later experiments 

 on the egg of the frog have shown that if the 

 cell is given an opportunity for a certain re- 

 arrangement of its protoplasm, there too a 

 complete but small embryo will result. The 

 evidence then instead of being contrary to 

 epigenesis is entirely in its favour. One last 

 series of experiments and we can turn to the 

 consideration of the bearing of these observa- 

 tions on the question of Vitalism. 



