94 MENDELISM chap. 



cases which have hitherto been regarded as following a 

 simple 3 : i ratio will turn out on further analysis to belong 

 to this more complicated scheme. 



This account of coupling and repulsion is based upon 

 the evidence from the sweet-pea, which has been more 

 carefully studied in this connection than any other species, 

 and it is not pretended that it offers more than a pre- 

 liminary account of these interesting and peculiar phen- 

 omena. Facts are known which are not entirely covered 

 by the scheme suggested. Baur,i f-Qj. instance, working 

 with Antirrhinum, has adduced evidence that in a case 

 where coupling in Y^ resulted from the cross AABB x aabb, 

 the converse cross AAbb x aaBB behaved in a normal 

 Mendelian manner without showing repulsion between 

 A and B. 



Lastly, we may ask whether these phenomena are con- 

 fined to plants or whether they are also to be found among 

 animals. That in certain animals something in the nature 

 of repulsion takes place between certain factors and the 

 sex factor will appear in the next chapter. And evidence 

 is beginning to accumulate suggesting that coupling and 

 repulsion may occur in animals independent of the sex 

 factor. Morgan's recent work on the inheritance of eye 

 colour and wing characters in the little pomace fly ^ {Droso- 

 phila) is strongly suggestive of the operation of coupling, 

 while Hagedoorn * has described the repulsion between the 

 factor for agouti (G) and that for colour (C) in a certain 

 strain of mice. Quite recently I have myself obtained 

 experimental evidence for the coupling of certain factors 

 influencing the coat colour of rabbits. Such evidence then 

 as we possess suggests that as we learn more of these 

 matters we shall find these phenomena under some form 

 or other playing an important part in the heredity of 

 animals. And, indeed, this is what, on general considera- 

 tions, we might have been led to expect. Among the 



1 Zeit. f. ind. Absi. u. Vererb., 1912. 

 ^ Journ. Exp. Zool. , 1 9 1 1 . 



2 Zeit. f. ind. Abst. u. Vererb., l<^\2,. 



