SEXUAL HORMONES AND MORPHOGENSIS 459 



find in Darwin, in the study of modern heredity a mere statical 

 or morphological way of thinking sometimes prevails. We 

 meet with a tendency to speak of male and female genetic 

 factors, corresponding to sex characters, and being present 

 simultaneously in male and female individuals; the individual 

 is phenotypically monosexual because the genetic factors of the 

 opposite sex are recessive or latent. If we assume the hypo- 

 thesis of an asexual embryonic soma there is no further need to 

 postulate special genetic factors for male and female sex 

 characters in mammals and birds, maleness and femaleness 

 being represented in the fertilized egg only by the single genetic 

 factor for the hormone-producing sex gland. 



It is easy to show that the three above-mentioned groups of 

 facts which at first sight seem to prove the presence of genetic 

 factors of both sexes in every individual can be explained also 

 on our hypothesis. 



(i) Tandler (Tandler and Gross, 1913, pp. 80, 81, 137) 

 pointed out that the rudiments of the Miillerian and Wolffian 

 ducts as present in both sexes prove the great phylogenetic 

 importance of these organs, but not the bisexuality of the soma. 

 According to Oscar Hertwig (1902, p. 413), the ductus Wolff ii is 

 regarded as an excretory duct which probably served simul- 

 taneously for the expulsion of the products of excretion of the 

 Wolffian body and of the generative cells of both sexes. As 

 Hertwig points out, similar conditions are to be found in 

 invertebrates, as for instance, in certain worms, where through 

 nephridia perforating the body wall not only various execretions 

 but also generative cells are expelled. Hertwig claims that in 

 vertebrates these two functions were taken up by two different 

 ducts, the ductus Wolfhi and the ductus Miilleri. And, 

 according to Tandler, it is easy to understand how the ductus 

 Wolfhi, being the excretory duct of the primary urinary 

 apparatus, is present in individuals of both sexes, though 

 later on losing its importance in the female. A similar line of 

 argument seems to be true also for the ductus Miilleri, which 

 evidently lost its significance in the male after the ductus 

 Wolffii had again taken up its original function of expelling the 

 excretions and with these the male generative cells. The 

 position may be expressed as follows: It is probable that the 

 ductus Wolffii and the ductus Miilleri originally served both 

 for the expulsion of the different excretions and of the 



