OPERATION OF THE GENETIC SYSTEM 73 



(XO) would thus produce one type of development 

 (toward the male), the secretion from the ovary (XX) 

 another type. Such suggestions have often been made. 



(12) Confirmation of the suggestion of diverse secre- 

 tions circulating in the body: the "free martin" — When 

 twins of opposite sexes occur In cattle, the male twin is a 

 normal, well-developed male. But the female twin Is usually 

 an "intersex"; It is intermediate in structure between the 

 male and female. It has many male characteristics, together 

 with some female characteristics. There are different grades 

 of intermixture, in different cases, and sometimes the fe- 

 male is normal. 



What is the cause of this partial transformation of the 

 female into a male? 



It was found by F. R. Lillie ■* that in all such cases there 

 is an intercommunication of the blood system of the two 

 twins, so that blood flows from the body of the male twin 

 into the body of the female, and vice versa. But in cases 

 where the female is normal, there Is no intercommunication 

 of the blood systems. 



From this it appears clear that the cause of the partial 

 transformation of the female into a male is this intercom- 

 munication. Blood flows from the body of the male into that 

 of the female, causing the latter to develop in the direction 

 of maleness. 



But why should It change the female only, not the male? 

 Why does the latter not become intermediate also? 



The answer to this question is given, with great probabil- 

 ity, by the fact noticed on an earlier page, that the male 

 begins the development of its distinctive sexual characteris- 

 tics earlier than does the female. The individual is recog- 

 nizable as male, before the female changes from the juvenile 

 condition. Hence the male begins to produce Its characteris- 

 tic secretion first. This then circulates into the female body, 

 and transforms it in the direction of maleness. As a result 



