220 WHAT 18 LIFE 



urchin soon after fertilization into a solution which 

 differed in specific points from sea-water, and found 

 that "when the eggs are allowed to segment in such 

 a solution the first two cleavage cells are as a rule in 

 a large percentage of cases — often as many as ninety 

 per cent — separated from each other, and when the 

 eggs are put into normal sea-water (about twenty 

 minutes after the cell division) each cell develops 

 into a normal embryo. "^^ Experimenting upon eggs 

 of the frog, it was found — first by Hans Driesch — 

 that if the first two cells of a dividing egg are sepa- 

 rated, each cell develops into a whole embryo of half 

 size. Driesch also found that by shaking a sea- 

 urchin's egg in the four-cell stage, the four cells may 

 be separated, and each one may develop into a com- 

 plete embryo, "which only differs in size from the 

 normal embryo." 



In Jacques Loeb's words: "Roux destroyed one 

 of the two first cells of a (fertilized) frog's egg with a 

 hot needle and found that as a rule the surviving cell 

 developed into only a half embryo. "^^ 



Again Loeb's words: T. H. Morgan "destroyed 

 one-half of the egg (fertilized frog's e^g) after the first 

 segmentation and found that the half which remained 

 alive gave rise to only one-half of an embryo, thus 



'^ The Organism as a Whole, 137. 

 36 /few/., 141. 



