WHAT EVOLUTION IS 89 



with '^ black" ovaries was paired 

 with a pure white male with the 

 result that between six to twelve 

 months after the operation she bore 

 two litters of young. These consisted 

 in all of six offspring every one of 

 which was black exactly as though a 

 black female had been paired with 

 the white male. This test shows that 

 after almost a year of residence in 

 the foster white body the ovaries 

 from the black female still retained 

 in full force their original potentiali- 

 ties and gave no evidence that the 

 new foster body had influenced them 

 in the least. This experiment sup- 

 ports Weismann's contention that the 

 germ cells are essentially independent 

 of the body in which they reside. 



But again it may be maintained 

 that the period over which such trials 

 extended was much too short for a 

 real test of the question and that, if 



