r 



II] Galton's Sy stern compared 55 



from whom he received a considerable series of letters and 

 illustrative specimens (197). These must have utterly failed 

 to arouse his interest, for when in 1884, the year of Mendel's 

 death, he published his great treatise on heredity, no refer- 

 ence was made to Mendel or his work. That this neMect 

 was due to want of comprehension is evident from a passage 

 where he describes an experiment or observation on cats, 

 which as it happens, gave a simple Mendelian result. The 

 Angora character (recessive) disappeared in a cross with a 

 certain common cat whose hair-character is, as we now 

 know, dominant. The cross-breds were mated together 

 and the Angora character reappeared in one individual 

 among a litter of common cats^. This typically Mendelian 

 fact was thus actually under Nageli's own observation, but 

 from the discussion which he devotes to the occurrence it 

 is clear that Mendel's work must have wholly passed from 

 his memory, having probably been dismissed as something 

 too fanciful for serious consideration. 



C It may be useful to specify the distinctive features of 

 Mendelian inheritance which differentiate the cases ex- 

 hibiting it from those to which Galton's system of calculation 

 — or any other systems based on ancestral composition — 

 can apply. 



(i) In Mendelian cases, in which the characters behave 

 as units, the types of individuals considered with respect to 

 any pair of allelomorphic characters are three only, two 

 being homozygous and one heterozygous ; while according 

 to such a system as Galton's the number of possible types 

 is regarded as indefinite. 



(2) The Mendelian system recognizes that purity of 

 type may be absolute, and that it may arise in individuals 

 of the 7% or any later generation bred from heterozygotes. 

 The views based on ancestry regard purity of type as 

 relative, and arising by the continued selection of numbers 

 of individuals. 



(3) In Galton's system no account is taken of domi- 

 nance, a phenomenon which plays so large a part in the 

 practical application of any true scheme of heredity. 



These distinctions are so definite and striking that at 

 first sight it seemed likely that the two methods might be 



* C. Nageli, MechaniscJi-J>hysioiugisc/ie Theorie der Abstammun^sUhre, 

 1884, P- 199- 



