SEX DETERMINATION 261 



odd cliromosome (when this occurs) as a sex-chromosome, or 

 an X-chromosome. But a moment's reflection will show (as 

 Morgan himself once suggested) that quantity of such sub- 

 stance may be quite as influential as quality in detennining 

 sex, since by h\T)othesis one X-chromosome produces a male 

 and two X-chromosomes a female, in species such as the 

 squash bug. The essential thing in sex determination is 

 probably not so much the possession of some particular sort 

 of material as the attainment of a particular grade of ana- 

 bolic capacity, femaleness implying a higher grade than male- 

 ness, since in the former condition macro-gametes are pro- 

 duced, whereas in the latter micro-gametes are produced. 



That maleness and femaleness are only different grades of 

 reproductive capacity is indicated by a study of organisms 

 in which the two functions are combined. In many of the 

 lower animals and in most of the higher plants, the same in- 

 dividual is capable of producing both macro-gametes and 

 micro-gametes. Sometimes these are produced simultane- 

 ously but in separate gonads, as in flatworms and leeches 

 among animals, and in " perfect " flowering plants. Such 

 parents are true and simultaneous hermaphrodites. Some- 

 times the individual may function at first as a male and later 

 as a female, a condition known as successive hermaphro- 

 ditism. This is found in certain worms and mollusks and in 

 the prothallia of certain ferns and mosses. This condition is 

 also approached in flowering plants such as cucumbers, 

 melons, and squashes, which at first produce only male blos- 

 soms but later produce those of both sexes. In other cases 

 the individual may function chiefly as of one sex but partially 

 as of the other sex. This condition is found in polygamo- 

 dioecious plants and exceptionally in such animals as cray- 

 fish, mollusks, worms, and even frogs and fishes, which, in a 

 particular part of an ovary may develop sperms, or in a 

 particular part of a testis may develop eggs. 



Such facts as these indicate that maleness and femaleness 

 are merely different grades of one and the same form of repro- 

 ductive activity. This is not inconsistent with their behavior 



