^22 Relation of Use and Disuse to Evolution 



from a black female) all the offspring were black. That 

 is to say, the white female did not modify the germ cells 

 produced in the foreign ovary which she carried in her 

 body. Nothing in the germ cells derived from a black fe- 

 male was influenced by the intimate lodgment and nourish- 

 ment in the body of the white female. The eggs continued to 

 " transmit " whatever it was they represented in their original 



Fig. 86. The Foster Mother as Environment 



The black female, top, had her ovaries removed and engrafted in the albino female, 

 left, which had been previously spayed. After recovery of the albino, she was mated 

 with the albino male, right. The offspring, bottom row, were all black and indis- 

 tinguishable, as to pigmentation, from the grandmother who had supplied the eggs. 

 The maturing, fertilization and development of the eggs seemed to be unaffected 

 by the character of the foster mother, so far as the pigmentation is concerned. After 

 Castle and Phillips; photograph by courtesy of Professor W. E. Castle. 



position in the body of the black guinea pig. Further breed- 

 ing and other experiments support this view: the germ cells 

 are not modified by the body. 



The thousands of experiments that followed the redis- 

 covery of Mendel's principles have still further confirmed 

 this conclusion, and supported Mendel's theory of the purity 

 of the germ plasm. The most intimate protoplasmic union 

 that we know is that between the chromosomes of the sperm 

 and those of the egg. Yet after this union it is possible for 



