234 GENERAL ZOOLOGY 



appear that the zygotic sex is the same as the definitive sex. 

 However, it has been conclusively shown that under abnormal or 

 under experimental conditions, the zygotic sex may be altered, or 

 completely changed. That amounts to saying that an animal 

 determined as a female at fertilization may be changed to a 

 definitive male or vice versa. Thus when the functional ovary 

 of a Brown Leghorn is removed early in life, the rudimentary 

 right gonad may develop into a testis and the bird takes on most 

 of the characteristics of the male. This seems to indicate that 

 the female in this case is heterozygous for sex, i.e., that it has the 

 potencies of both male and female sex organization. This is not 

 true of the cock, where removal of the testes does not produce a 

 female, but a kind of neutral condition known as the capon. In 

 the female the presence of the normal ovary and, as a result, the 

 presence of hormones secreted by the ovary, exercise a restraining 

 influence on the development of inherent male potencies. Hens 

 in their old age sometimes crow like cocks, a condition that also 

 seems to be due to the removal of active ovarian tissue through 

 atrophy. There is at least one authentic case on record of a hen, 

 after having laid eggs that produced normal chicks, changing into 

 a cock that became a functional male in all respects even to the 

 point of "fathering" two chicks. In this case postmortem 

 examinations showed that the ovary had been destroyed by 

 tuberculosis. 



There is nothing specific in the X or Y chromosome as sex 

 determiners. Neither is endowed with what might be called 

 exclusive qualities of maleness or femaleness. Some observations 

 indicate that the result of normal XX or XY combinations seems 

 to rest on the relative proportion of autosome to sex chromosome 

 material. Thus the presence of XX or XY in Drosophila does 

 not necessarily produce a female or male, respectively. Studies 

 of flies in which abnormal chromosomal combinations had been 

 formed as a result of nondisjunction in the maturation divisions, 

 shows that flies with 2 X chromosomes but with 3 each of the 

 autosomes, making a total of 11, are not females but intergrades 

 between males and females. The tendency toward maleness in 

 such cases would seem to be due to the fact that there is less X 

 chromosome material in proportion to autosomes than is present 

 in normal females. In other words, sex factors exist in the 

 autosomes as well as in the "sex" chromosomes. 



