INHERITANCE 197 



revealed the fact that the second and third chromosomes 

 were present in triplicate, while an additional fourth chromo- 

 some was present in some but lacking in others, there being 

 thus two degrees of the triploid condition, that with three 

 fourth chromosomes being more female (Morgan, Bridges and 

 Sturtevant, 1925). The X chromosome was present in dupli- 

 cate in the intersexes but the females possessed three X 

 elements. Thus using the symbol A for autosome and X 

 for the sex-chromosomes, the genetical constitution of these 

 intersexes and abnormal females were respectively 3A-I-2X 

 and 3A4-3X, as contrasted with the normal female con- 

 stitution 2A -h 2X. Abnormal males were also found with the 

 constitution 3A-hX, as contrasted with the normal male con- 

 stitution 2A + X. Therefore if X : A= i or> i the individual 

 is a female, if X : A | or<-| it is a male, but when X : A lies 

 between the i and | the intersexual condition is manifested. 



General Validity of the Factorial Hypothesis.— The fac- 

 torial hypothesis has aroused a good deal of hostility, not 

 unnaturally, for it conflicts with many accepted speculations 

 as to the evolution of living organisms and throws doubt on 

 not a few beliefs still current in the medical profession. The 

 remarkable diversity of inherited characteristics, anatomical 

 and physiological, with which it deals ; the truly amazing 

 correspondence between the conclusions derived from experi- 

 mental and microscopic studies ; and finally, the established 

 fact that the nucleus is the only recognisable cell-element 

 which is universally contributed by the sperm to the develop- 

 ment of a new individual can leave little room for doubt in 

 the minds of impartial students of the subject that, in broad 

 general outline, it will be found to apply to all the essential 

 phenomena of biparental inheritance. If this is so its 

 importance for the study of animal function does not lie merely 

 in the account it gives of the contribution which the male and 



