S04 The Unity of the Organism 



tion by budding from a wound." ^ 



Driesch went on with his sea-urchin eggs, as Roux had 

 with the frog-eggs, to see what cells would do if separated 

 in the four-cell stage. He found that such cells could also 

 give rise to whole larvae, Taut of correspondingly diminished 

 size. So far then, as the sea-urchin is concerned, taking 

 the facts at their face value, the cells of the very young 

 embryos were proved to be diametrically the opposite in 

 their relation to the complex as a whole, from the individual 

 stones of a mosaic work. 



Driesch's methods of treating developing eggs were soon 

 much resorted to by other investigators, with the general 

 outcome that numerous animals in widely separated parts 

 of the animal kingdom were proved to have much the same 

 developmental ability as the sea-urchin. Wilson found that 

 the cells of Amphioxus embryos separated in the two- and 

 four-cell stage would develop from the very he ginning after 

 isolation like whole eggs of reduced size. It will be recalled 

 that the sea-urchin cells separated by Driesch developed 

 at the beginning like half-eggs, and only changed over to 

 the whole-embryo in the blastula stage. So Wilson's dis- 

 covery removed Amphioxus still farther from the mosaic 

 type of development than the sea-urchin had been removed 

 by Driesch. 



The Italian zoologist, Raffaello Zoja, increased knowl- 

 edge of whole-animal production from a portion of the cells 

 of the young embryo, by showing that in the hydroid Clytia 

 ftazidula, not only one of the blastomeres from the two-cell 

 stage, but one from the four- and eight- and even the six- 

 teen-cell stage, will develop to complete organisms of dimin- 

 ished size, the half and the fourth at least, of the whole egg, 

 being capable of going on with the development until the 

 adult animal, perfect except as to size, is reached. 



In view of the fact that the egg of the frog, a representa- 

 tive of one of the two main sections of the Amphibia (the 



