68 INHERITANCE IN RABBITS 



in F! black offspring, and in F 2 black, blue, red, and cream, as well as 

 albinos; whereas the latter produces in F t cream, and in F 2 cream and 

 albino offspring only. 



As regards the factor U, Hurst ( : 05) has shown clearly that some albino 

 rabbits transmit a uniformly colored coat, others a spotted coat, in crosses 

 with colored rabbits. The former we may regard as carrying U, the latter 

 S. In rabbits we have not made an extensive study of this matter. We 

 have found, however, in agreement with Hurst, and Woods (:O3) that 

 spotted rabbits in general produce only spotted young, when mated with 

 each other, i. e., that spotting with white is recessive to uniform pigmenta- 

 tion, and the case has been mentioned of an albino (c? 45) which produced 

 spotted young when mated with a black rabbit that had a spotted father. 



In guinea-pigs also, spotting is in the main recessive, and spotting is 

 clearly transmitted by albinos. Thus the <? 2002, figured and described 

 by Castle (: 05), produced spotted young when mated with spotted females, 

 and among his grandchildren spotted animals were very common, no matter 

 whether the female grandparent and the parents were spotted or not. 



All the varied evidence which has been obtained from the study of 

 rabbits, guinea-pigs, rats, and mice, by others as well as by ourselves, 

 supports the hypothesis that albinos differ from pigmented individuals, 

 by a single factor only, which factor we call C. 



THE MATERIAL BASIS OF HEREDITY FACTORS. 



In what form, it may be asked, are we to suppose that the various 

 assumed factors exist. Do they occur as so many different substances 

 lying side by side but unmixed in every reproductive cell? To this ques- 

 tion we may give at present no satisfactory answer. 



It is, however, we think, not necessary to suppose that there exist in 

 the minute germ-cell as many complex organic substances as there are 

 activities of the cell; neither is it necessary to suppose a different substance 

 present for every independent factor identified. The various indepen- 

 dent factors may have a basis no more complicated than that of so many 

 atoms attached to a complex molecular structure. Experiment shows that 

 the factors may be detached one by one from the organic complex. The 

 discontinuity of their coming and going is entirely in harmony with the 

 conception of them as components merely of complex molecular bodies. 



