EVOLUTION BY LOSS 



entific expectation in the case was published, 

 and a few months later I had the satisfaction 

 of announcing its fulfillment in the second gen- 

 eration (F 2 ) from the cross in question. 



The experiment progressed as follows : The 

 parents were an agouti and a black, their F x 

 offspring were agoutis in character ; but the F 2 

 offspring were of four sorts, agouti, black, 

 cinnamon, and brown. The cross thus produced 

 two varieties new to the experiment, viz. black 

 and cinnamon, the latter being a variety at 

 that time new among guinea-pigs. 



The subsequent behavior, too, of the newly 

 produced cinnamon variety is in harmony 

 with expectation based on Mendelian prin- 

 ciples. The cinnamon variety has not pro- 

 duced agouti or black individuals, which from 

 the formulae it will be seen it may not be ex- 

 pected to produce, since it lacks the factor B. 

 But it has in some cases produced brown in- 

 dividuals, as it clearly could in case both par- 

 ents to a mating were heterozygous (single) 

 in factor A. 



On the whole the evidence seems very clear 

 that the numerous color varieties of animals 

 7 85 



