24 GENETICS AND EUGENICS 



of the home, and are themselves unmodified bv those activi- 

 ties. To show the biological soundness of Weismann's con- 

 clusion that soma and germ-plasm are anatomically and 

 physiologically distinct, I may cite an experiment performed 

 by Dr. John C. Phillips and myself: 



A female albino guinea-pig (Fig. 3) just attaining sexual maturity was 

 by an operation deprived of its ovaries, and instead of the removed ovaries 

 there were introduced into her body the ovaries of a young black female 

 guinea-pig (Fig. 2), not yet sexually mature, aged about three weeks. The 

 grafted animal was now mated with a male albino guinea-pig (Fig. 4). 

 From numerous experiments with albino guinea-pigs it may be stated 

 emphatically that normal albinos mated together, without exception, pro- 

 duce only albino young, and the presumption is strong, therefore, that had 

 this female not been operated upon she would have done the same. She 

 produced, however, by the albino male three litters of young, which to- 

 gether consisted of six individuals, all black. (See Figs. 5-7.) The first litter 

 of young was produced about six months after the operation, the last one 

 about a year. The transplanted ovarian tissue must have remained in its 

 new environment therefore from four to ten months before the eggs at- 

 tained full growth and were discharged, ample time, it would seem, for the 

 influence of a foreign body upon the inheritance to show itself were such 

 influence possible. 



Since, then, germ-cells and body are distinct, heritable 

 variations cannot have their origin in body-cells but only 

 in the germ-plasm. The problem of evolution, therefore, on 

 Weismann's view, becomes this — how are changes in the 

 germ-plasm brought about ? 

 Darwin's theory of ^pangenesis. 



Before Weismann's time, Darwin, in common with biolo- 

 gists in general, had come to recognize that the germ-cells 

 (i. e., the egg and sperm-cells) are the sole vehicles of inheri- 

 tance. Darwin therefore realized that if acquired characters 

 are inherited, as everyone then supposed, bodily modifica- 

 tions must in some way be registered in the germ-cells, and 

 he framed an hypothesis to explain how this could come 

 about. This hypothesis, which he called Pangenesis, is put 

 forward in the closing chapters of his book on Animals and 

 plants under domestication. Darwin himself was not sure 

 of its correctness and advanced it as he says " tentatively " 

 only. We are very sure that it was not correct, but it has for 



