782 



NATURE 



[August 18, 192 1 



as experiments show, develop into a female, a 

 male, or something between. Finally, if it be 

 assumed that the strong races are possessed of 

 sex-factors of a higher absolute quantity, the pro- 

 duction of intersexuality in the crosses is also 

 explained — the big dose of a male factor con- 

 fronted as the result of crossing with a dose of 

 the female factor which is relatively too small 

 determines the character of the offspring even in 

 the one-dose (X) state. As a matter of fact, 

 all the breeding experiments devised to test such 

 views have given results in accordance with 

 theory. 



Fortunately, the analysis of the intersexual in- 

 dividuals could be pushed one step further towards 

 a physiological understanding. It could be 

 demonstrated by a very large number of really 

 amazing morphological and em- 

 bryological facts that intersexual 

 females are individuals which 

 had developed up to a certain 

 moment as females, when sud- 

 denly the sex had changed and 

 development was finished as a 

 male. Similarly, intersexual 

 males begin as males and end as 

 females, and the different types 

 of intersexuality were proved to 

 be the consequence of the posi- 

 tion of the turning point in 

 development. A late turning 

 point means that only certain 

 organs, which have not com- 

 pleted their development, can be 

 forced into the line of differentia- 

 tion of the other sex ; the result 

 is an intersex <5f low grade. An 

 earlier position of the turning 

 point consequently leads to the 

 production of the higher grades 

 of intersexes, and a still earlier 

 position to the complete reversal 

 of sex. The degree of inter- 

 sexuality is inversely proportional to the posi- 

 tion of the turning point in the progress 

 of development. The position at this point 

 of the analysis is this : on one hand we 

 have the presence of characteristic doses of 

 substances called sex-factors in definite quan- 

 tities ; on the other, there is a period of 

 varying duration (the time of development 

 up to the turning point), the length of which 

 is proportional to the difference in the quantities 

 of the two sex-factors. This points emphatic- 

 ally to the idea that the sex-factors are 

 substances which cause, take part in, or 

 accelerate a reaction in proportion to the quantity 

 present. The result may then be represented in 

 the graph (Fig. i) : on the abscissa is plotted the 

 time of development, the line i-i being the end 

 of embryonal and larval differentiation. The 

 ordinate indicates the amount of that product of 

 the activity of the sex-factors which carries differ- 

 entiation in the direction of one sex. The curve 

 F shows the rate of production of the female- 

 NO. 2703, VOL. 107] 



determining substances, which is constant for each 

 *^&& of a given race. Mm is the curve for the 

 male-determining substances in the female (one 

 dose, X) ; MM in the male (two doses, XX). 

 In normal reproduction the F and M curves 

 do not intersect in development. Mitn, Mgm, 

 etc., are the curves of the male-determining sub- 

 stances produced by the larger quantities of M 

 substance in the X -chromosomes of the strong 

 races. Their points of intersection with the F 

 curve (in the case of hybrid combination) occur 

 during development, and represent the turning 

 point where sex changes from femaleness to male- 

 ness. The graph then gives the physiological solu- 

 tion of the case of intersexuality ; simultaneously 

 it answers the question which led to the considera- 

 tion of the work on intersexuality — viz. : How does 



"Time o[ development 



FiO. I. 



the presence of one or two X-chromosomes con- 

 taining sex-factors act physiologically in order to 

 induce the differentiation of one or the other sex? 

 The answer is : The mechanism which produces 

 germs with two and one X respectively is an ideal 

 mechanism to secure the higher velocity to one 

 or the other of two simultaneous and competing 

 reactions, namely, the male and female reaction, 

 by starting it with the greater quantity of reacting 

 substance. 



But there is a limit to our analysis so far as 

 the work on intersexuality is concerned. We can 

 see no means of ascertaining in moths in what 

 this reaction, the velocity of which is influenced by 

 the concentration of the reacting substances, really 

 consists. The answer can be given, we believe, 

 by the facts of hormonic intersexuality. 



It is well known to every student of biology 

 and physiology that in the higher vertebrates, at 

 least in birds and mammals, the endocrine func- 

 tion of the sex-gland plays an important rdle in 

 the development of secondary sex-characters. 



