CORRELATION OF ENDOCRINE GLANDS WITH SEX DIFFERENTIATION 889 



c. Possible Influence of the Sex Field in Sex Determination 

 Two gonadal sex fields, the cortical field and the medullary field, are 



present in the early vertebrate gonad in amphibians, reptiles, birds, and 

 mammals. This condition is true also of many fishes. Sex differentiation pri- 

 marily is a question as to which one of these fields will assume dominance. 

 During development in various instances, sex differentiation is clearly the 

 result of only partial dominance on the part of one sex field, the other field 

 emerging partly or almost completely. As a result, various types of intersexes 

 may appear. For example, in the male toad. Bidder's organ at the anterior 

 part of the testis represents a suppressed cortical or ovarian field, held in 

 abeyance by the developing testis. Surgical removal of the two testes permits 

 the cortical field or Bidder's organ to become free from its suppressed state. 

 As a result, functional ovaries are developed, and the animal reverses its sex, 

 becoming a functional female (Witschi, '39). 



One of the classical examples which demonstrates the dependence of the 

 developing sex field upon surrounding environmental factors is the freemartin. 

 The freemartin appears in cattle when twins of the opposite sex develop in 

 such a manner that an anastomosis or union of some of the fetal blood vessels 

 occurs (Lillie, '17). Under these circumstances the female twin always ex- 

 periences a transformation in the direction of maleness in the gonad and sex 

 ducts. In those instances of freemartin development where the cortical field 

 of the developing ovary is suppressed and the medullary area is hypertrophic, 

 a partial or fairly well-developed testis may be formed. Under these conditions 

 it is presumed that some substance is elaborated within the medullary field of 

 the developing gonad of the male twin which enhances the development of 

 the similar field in the freemartin ovary and suppresses, at the same time, 

 the cortical field. The development of fully differentiated gametes (i.e., sperm) 

 in the freemartin "testis" has not been demonstrated, but, on the whole, the 

 more normally developed freemartin testis shows conditions at the time of 

 birth which are comparable to a similar gonad of the normal male at about 

 the same age, with the questionable presence or absence of very young germ 

 cells. Gametogenesis in the developing testis of the bull occurs after birth. 

 Consequently, the development of gametes in the freemartin of cattle cannot 

 be ascertained because the freemartin gonad remains in the position of the 

 normal ovary and does not descend into the scrotum as it does in the male 

 (Willier, '21 ). A scrotal residence (Chap. 1 ) is necessary for spermatogenesis 

 in all males, possessing the scrotal condition. 



A particularly interesting case of intersexuality, resulting from the lack of 

 complete supremacy on the part of one sex field, is shown in the fowl described 

 by Hartman and Hamilton ('22). A brief resume of its behavior and anatomy, 

 as described by the authors, is presented herewith. 



The bird was hatched as a robust chick and developed into an apparently normal 

 Rhode Island Red pullet. The following spring the comb and wattles began to 



