48 Rights and Lefts [ch. 



Respecting the genetics of one most interesting class 

 of variations evidence is scanty. This is right- and left- 

 handedness. From Mayer's^ observations on Partula 

 (Gastropod) we learn that parents of either twist may bear 

 young of either twist. The numbers in the uteri were so 

 small that the absolute numbers are insignificant, and it 

 may be an accident that no mixture of types was found in 

 anyone uterus. Langf bred numerous left-handed Helix- 

 pomatia with each other and obtained thousands of young, 

 all right-handed, which in their turn again produced ex- 

 clusively right-handed offspring. Direction of twist is a 

 fundamental meristic phenomenon, being, as Crampton and 

 Conklin have proved, determined as early as the first 

 cleavage-plane in the ^<g^ ; and great light on the problems 

 of cell-division might perhaps be obtained if the inheritance 

 of these differences could be determined. The only case 

 we have attempted to study, that of Medicago, in which the 

 fruits are right- or left-handed spirals according to species, 

 proved unworkable, perhaps on account of the minute size 

 of the flower and the roughness of the manipulations. 



Lutz (181) has collected facts as to the inheritance of 

 the mode in which the hands are clasped, whether the right 

 or left thumb is placed uppermost. No definite result was 

 obtained, but effects of heredity were somewhat marked, 

 though neither condition bred true. Lutz kindly tells me 

 that a full analysis was made, taking families separately. 



When the Mendelian principles were first rediscovered 

 the suggestion was made that though the system might 

 apply to the unions of pure races, there was no certainty 

 that such rules apply to the uncontrolled matings of natural 

 forms. The objection was not one which was likely to 

 have weight with those who had -an acquaintance with 

 genetic phenomena, but it had undoubtedly an effect in post- 

 poning general recognition of the importance of Mendel's 

 discovery. Categorical proof of the invalidity of this ob- 

 jection is now provided by one of the cases referred to 

 above — that which concerns the heterostylism of Primula. 

 It is scarcely doubtful that in the Primrose nearly every 

 plant arises by the ** legitimate " union of long- and short- 



* Mayer, A. G., Mem. Miis. Comp. Zool. Harvard, xxvi. No. 2, 1902. 

 i" Lang, A., Vierteljahrs. d. ?iat. Ges. Zurich, 1896, and 168, p. 42, 

 together with information kindly sent in a letter. 



