Proceedings of the Ohio State Academy of Science 341 



which may be expressed in one form or another during develop- 

 ment from the egg on up to the death of the individual. 



TIME OF DETERMINATION OF THE SEX OF THE INDIVIDUAL. 



Nothing in biology is more definitely established than the 

 fact that there is no definite or special time common to all or- 

 ganisms at which the sexuality of the individual is determined. 

 It may be in the vegetative cells before the sporocytes are pro- 

 duced, in the development of the sporocytes themselves, in the 

 daughter cells of the sporocytes, or at some later stage. In the 

 case of organisms with the diploid number of chromosomes, the 

 sex may be determined in one of the gametes before fertilization, 

 and for the individual, therefore, at the time of fertilization, or 

 in certain species at some subsequent time. 



In speaking of the determination of sex, one must not for- 

 get that there are a number of types of sexual individuals, — 

 namely, haploid males, females, and hermaphrodites; diploid 

 males, females, and hermaphrodites ; and of heterosporous 

 sporophytes there are diploid microsporangiate, megasporangi- 

 ate, and bisporangiate individuals. Through parthenogenesis 

 there are possibly also haploid microsporangiate, megasporangi- 

 ate, and bisporangiate individuals. In all critical discussions 

 these different categories must be clearly distinguished before 

 generalizations can be made. 



Recently the opinion has several times been expressed that 

 it is wrong to compare hermaphrodites which have in a given 

 case developed but one sex with what are supposed to be true 

 unisexual forms. But the stand does not seem to be well taken. 

 We have all gradations between normal hermaphrodites and 

 true unisexual gameophytes as well as between bisporangiate 

 and monosporangiate sporophytes. Many of the discussions on 

 sex-heredity are confused because the authors fail to recog- 

 nize the logical homologies between sexual and nonsexual plants 

 and animals. The most common mistake along this line is in 

 regard to the haploid gametophyte generation which has no clear 

 homolog among the animals. The same confusion exists in re- 



