EXPERIMENTAL MORPHOGENESIS 59 



wanted a proof, and with this intention he carried out 

 an experiment which has become very celebrated. 1 With a 

 hot needle he killed one of the first two blastomeres of 

 the frog's egg after the full accomplishment of its first 

 cleavage, and then watched the development of the surviving 

 cell. A typical half- embryo was seen to emerge an organ- 

 ism indeed, which was as much a half as if a fully formed 

 embryo of a certain stage had been cut in two by a razor. 

 It was especially in the anterior part of the embryo that 

 its " halfness " could most clearly be demonstrated. 



That seemed to be a proof of Weismann's and Eoux's 

 theory of development, a proof of the hypothesis that there 

 is a very complicated structure which promotes ontogeny 

 by its disintegration, carried out during the cell divisions 

 of embryology by the aid of the process of nuclear division, 

 the so-called " karyokinesis." 



To the dispassionate observer it will appear, I suppose, 

 that the conclusions drawn by Eoux from his experiment 

 go a little beyond their legitimate length. Certainly some 

 sort of " evolutio " is proved by rearing half the frog from 

 half the egg. But is anything proved, is there anything 

 discovered at all about the nucleus ? It was only on 

 account of the common opinion about the part it played 

 in morphogenesis that the nucleus had been taken into 

 consideration. 



Things soon became still more ambiguous. 



THE EXPERIMENTS ON THE EGG OF THE SEA-URCHIN 



Eoux's results were published for the first time in 

 1888 ; three years later I tried to repeat his fundamental 



1 Virchows Archiv. 114, 1888. 



