42 Heredity and Eugenics 



A young female albino guinea-pig approaching sexual 

 maturity was deprived of her ovaries, and into her body 

 was introduced the living ovary of a freshly killed black 

 guinea-pig, about three weeks old (Figs. 7 and 8). She 

 was later mated with an albino guinea-pig (Fig. 9). 

 By him she bore two litters of living young, and died 

 pregnant a little over one year after the operation, con- 

 taining a third htter (Figs. 10-15). Had she not been 

 operated upon, her young by this male would undoubtedly 

 ha\'e been albinos, for albino guinea-pigs produce only- 

 albino young, as several in\'estigators have clearh' shown. 

 But those young which she did bear were without exception 

 black, which character clearly they owed to the fact that 

 they developed from eggs produced by the ovary taken at 

 a very immature stage from a black animal. From evi- 

 dence such as this it is concluded that the inheritance can 

 not be affected by modifications of the body of the parent, 

 not even when the body is completely changed, since the 

 body, so far as heredity is concerned, is merely a container 

 of the reproductive cells. To modify the inlieritancc we must 

 modify tlic reproductive cells. 



But the reproductive cells are not simple; they are 

 really dual in character, made up of ecjuivalent parts 

 derived from father and mother. On this matter breeding 

 experiments throw light. 



If a black guinea-pig of pure race is mated with an 

 albino, the offspring are all black, yet contain albinism as 

 a latent or recessive character. For if one of these black 

 offspring is now mated with the same albino, only Jialf of 

 the oft'spring are black, the others being albinos. And if 

 two of the cross-bred blacks are mated with each other, 

 one-fourth of the young, on the average, are albinos, three- 



