344 SEX IN MICROORGANISMS 



always perfect however, since in Trichonympha Cleveland sometimes 

 found intersexes or "gynandromorphs" among the "gametes." 



Just how far the application of this process can be extended is 

 problematical. Prokofieva-Belgovskaya applied the principle to the 

 segregation of "male" from "female" sets of chromosomes in various 

 Protozoa such as Actinophrys sol (Belaf, 1923, 1926), A?noeba dip- 

 loidea (Hartmann-Schilling, 1917), Adelea ovata (Jollos, 1929), 

 Stylorhynchus lojigicollis (Leger, 1904), and Bursaria truncatella 

 (third division of the micronucleus, Poljansky, 1934), as well as to 

 various other animals and plants. Prokofieva-Belgovskaya also sug- 

 gested that the segregation of "mother" from "daughter" chromo- 

 somes was the initial step in the evolution of "sex." Is the "mother- 

 daughter" system in the potato cells a sex-segregating system? If not, 

 why does it occur? Is that system of duplication a general one? In 

 Cleveland's flagellates, sex-segregating mitoses take place only under 

 the influence of the molting hormone of the host; at other times the 

 ordinary type of mitosis takes place. Cleveland's cases apparently 

 show that there are, then, two types of mitosis, a sex-segregating 

 type and a non-segregating type. What the stimuli to segregation 

 would be in a potato cell, or in the other cases cited by Prokofieva- 

 Belgovskaya, is not apparent. 



Although heterocyclicity may indicate sex difl"erences, and many 

 other instances could be cited, it does not necessarily indicate that 

 "mother-daughter" origin and separation of complete sets of chro- 

 mosomes are always required to differentiate the sexes. A difference 

 of one chromosome, or a part of a chromosome, or even one or a 

 few genes may be enough to differentiate male and female nuclei 

 from each other. The heterocyclicity, then, could well be the re- 

 sult of sex-determining influences other than the "mother-daughter" 

 system. 



In a note appended to the paper by Prokofieva-Belgovskaya, H. J. 

 Muller remarks that, if such mother and daughter chromosomes are 

 distinguishable, it would be most surprising if all the mother chromo- 

 somes should go to one pole and all the daughter chromosomes to the 

 opposite pole of the spindle. Although such a segregation is possible, 

 it would involve a new principle which might be as important as the 

 apparent differences between the two sets of sister chromosomes. It 

 remained for Cleveland to describe a mechanism whereby such a 

 segregation actually takes place. 



