TADACHIKA MINOUEA 



INTRODUCTION 



The study of the free-martin by F. R. Lilhe ('17 b) has thrown 

 new hght on the field of the biology of sex, demonstrating that 

 sexual differentiation is controllable, at least to some extent, 

 by a certain physiological factor. Lillie discovered that in the 

 free-martin, the female of two-sexed twins in cattle, the sex- 

 glands and sex-ducts are modified from the normal female con- 

 dition to a sterile masculinized state; that in cattle twins an 

 anastomosis of the umbilical blood-vessels exists between the 

 two embryos, and that this anastomosis is responsible for the 

 alteration of the female twin, the sex-hormones from the male 

 twin being thus enabled to gain access to the female twin through 

 the blood current and to produce a profound modification of her 

 reproductive system. A histological study of the same material 

 by Chapin ('17) supported Lillie's conclusion that the free-martin 

 is a modified female. As Lillie suggested ('17 a), "the possibility 

 exists, however, that definitely planned experiments may enable 

 us to regulate time and dosage of hormones better than is done 

 in this experiment of nature; the results of such experiments 



cannot of course be foreseen Such experiments will 



be necessary for the full solution of the stated problem." I 

 therefore, at Professor Lillie's suggestion, undertook to perform 

 such a series of experiments for the purpose of determining 

 whether or not sexual differentiation is experimentally control- 

 lable through the secretion of the sex-glands. Gonads were 

 grafted on the membranes of developing chick embryos in rela- 

 tively young stages; such embryos were then allowed to develop 

 further, and in cases where the grafts grew, the urinogenital 

 systems of the embryos were studied to determine what effects 

 had been produced by the presence of the gonad grafts. The 

 results of these experiments are presented in the present paper 

 and others to appear subsequently. 



It has already been abundantly proved through numerous 

 studies on birds and mammals that the sex-glands do produce a 

 secretion or secretions which play an important role in the pro- 

 duction and maintenance of secondary sexual characters. This 

 literature is so familiar to every one that it will not be reviewed 



