THE DUALITY OF INHERITANCE 



occurred even after the egg had undergone 

 maturation, being reduced to the N condition. 

 From the development of such reduced but 

 unfertilized eggs fully normal sea-urchins have 

 been obtained which even contain developed 

 sexual glands. On the other hand it has been 

 found possible to break the egg into fragments 

 by shaking it, or cutting it into bits with fine 

 knives or scissors. It has also been found 

 possible to bring about the development of 

 an egg fragment so obtained, a fragment 

 which contained no egg nucleus. This result 

 has been attained by allowing a sperm to enter 

 it and form there a nuclear body. No adult 

 organism has yet been reared from such a 

 fertilized egg-fragment, but so far as the de- 

 velopment has been followed it progressed 

 normally. 



There can accordingly be no doubt that the 

 nuclear material of a sperm-cell has all the 

 capabilities of that of an egg-cell and can in- 

 deed replace it in development. Accordingly, 

 when, as in normal fertilization, both an egg 

 nucleus and a sperm nucleus are present in 

 the cell, a double dose of the necessary nuclear 



19 



