48 Rights and Lefts [CH. 



Respecting the genetics of one most interesting class 

 of variations evidence is defective. 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 

 any one uterus. 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 egg ; 

 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. A fuller analysis 

 should be attempted, 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- 

 styled individuals. Yet the long-styled are always pure. 

 Moreover, all the short-styled plants hitherto tested have 

 proved to be simple heterozygotes, giving equality of longs 

 and shorts when bred with longs. Hitherto no pure DD, 



* Mayer, A. G., Mem. Mus. Comp. ZooL Harvard, xxvi. No. 2, 1902. 



