Mr BATESONS EEVISIONS OF MENDEL'S 

 THEOKY OF HEREDITY. 



By w. f. R. weldon, f.r.s. 



The results which Mr Darbishire has so far obtained by crossing pink-eyed 

 piebald waltziiig mice with normal pink-eyed albinos have beeu rccorded in 

 the last two numbers of Biometrika. In Nature of March 19 aud April 23 

 Mr Bateson has stated his belief that the inheritance of eye-colour iu these mice 

 is "strictly Mendelian," and lio has pnblished a Mendelian formnla which implics 

 his beiief that the inheritance of coat colour is Mendelian also. In order to 

 fidly understand Mr Bateson's treatment it is necessary to realise not only 

 Mendels own doctrines, bnt the various moditications of these which Mr Bateson 

 has from time to time propounded. Only after such preliminary survcy can we 

 discuss the bearing of the facts established by Mr Darbishire in his work ou 

 mice. 



Mendel's Theory of Hyhnds. 



Mendel made two general Statements, describing the results which he says he 

 invariably obtaineil in his experiments with cross-bred peas ; the first is what is 

 oftcn callcd his Law of Dominance, and describes the manner in which chanictcrs 

 are transmitted from the pure-bred parents to the hybrid resulting from their 

 uninn; the second is his Law of Segregation (Spaltungsgesetz, Loi de Disjonction) 

 and describes the characters of the subsequent generations, descended from the 

 hybrids originally produced ; to account for the phcuomena described by his Law 

 of Segregation, he puts forward a theory of the Constitution of the germ-cells, both 

 in pure-bred individuals and in hybrids. 



Mendel was the first to systeinatically anal^'se the difforential characters of 

 a race or species into a series of unit-characters, each of which might, uuder 

 suitable conditions, be inherited independently of the others ; in this he anticipated 

 the essential features of the view afterwards developed (without knowledge of 

 Mendels work) by de Vries. Mendel furthcr anticipated speculations of de Vries 

 and Weismanu by attributing the inheritance of each uuit-characler to the 



