DIFFERENTIATION, HEREDITY, SEX 315 



The idea that the relation between the chromosomes and 

 sex characters parallels that between the chromosomes and 

 any other traits involves the conclusion that sex is a character, 

 or group of characters, inherited in the same way that other 

 bodily traits are. And this conclusion may now be accepted. 

 Indeed there are in the field several hypotheses as to the precise 

 statement, of a Mendelian formula according to which sex is 

 inherited, and while no one of them has a preponderance of 

 evidence in its favor, the fundamental fact of sex heredity is 

 clear. 



There are extant scores of hypotheses regarding the factors 

 and processes involved in sex determination, depending upon 

 the action of conditions outside of the germ itself. These must 

 be abandoned when the facts now known to be true of the 

 germinal structure of a comparatively limited number of 

 species, gain a wider applicability. For the sex of an organism, 

 as well as other fundamental characters, appears to be already 

 determined in the zygote, and all that external conditions can 

 do toward determining sex is to alter sex ratios by affecting 

 differentially (selectively) the gametes or immature organisms 

 of a certain sex. 



There is some evidence of other kinds that sex is determined 

 in the gamete and not by external conditions. In certain 

 cases a single egg indirectly gives rise to a number of embryos 

 or larva? (multiple embryo formation) which are all of one sex, 

 either male or female. Silvestri describes such a case in the 

 development of a Hymenopter, Litomastix, parasitic in the 

 larva of a Lepidopter, Plusia, where as many as one thousand 

 embryos, all of one sex, are thus formed. And there is good 

 reason for believing that the embryos of one of the armadillos, 

 described by Newman and Patterson, are all derived from a 

 single ovum, and these are always of one sex only, either male 

 or female. There is also the familiar example of the bees 

 (Dzierzon), where unfertilized eggs develop parthenogenetically 

 into males (drones), while the fertilized ova produce females 

 (queen and workers) ; the same thing is apparently true of most 

 ants. And in one of the rotifers, Hydatina, a certain kind of 



