SEX IN PROTOZOA I53 



w hich niciosis, gamete fornuuion, and syngani)' can be accomplished. 

 These variations allow for an analysis of the process of meiosis and 

 an evaluation of the differences between meiosis and vegetative mito- 

 sis. Diploidv and polvploid\' mav arise tiirough chromosome duplica- 

 tion without centriole duplication as \\ ell as through syngamy. The 

 series of papers on indixidual genera and species gives tiie important 

 details. 



In preparing these re\iews of Cleveland's published papers, I 

 have, to a large extent, adopted my own phraseology. In doing so 

 there has been the risk of failing to convey the exact meanings that 

 Cleveland had in mind. It is to be understood, therefore, that I am 

 assuming full responsibility for the statements made in these reviews. 

 Naturally, limitations of space have made it necessary to omit a great 

 manv important aspects of Cleveland's work; hence the reader is 

 urged to read the original papers in order to appreciate their full im- 

 portance. 



Folyniastigotes. In three separate papers Cleveland described 

 the sexual behavior of members of the genera Oxyvwiias (1950a), 

 Siiccinobdciilus (1950b), and Notila (1950c), all belonging to the 

 Polymastigina. These three genera are closely related, each having 

 four anterior flagella, intranuclear centrioles, flat, rather broad axo- 

 styles, and a relatively large number of chromosomes. In Oxymojias 

 (Fig. G, 1 to 4) and Saccmobacuhis (5 to 6) the sexual cycles are 

 very similar. In each the animals are haploid, and gametogenesis con- 

 sists of the division of a gametocyte (1) (which before the division 

 cannot be distinguished from an ordinary agamont) into two gam- 

 etes which are only slightly dissimilar in size. During this division in 

 Oxymonas doroaxostyhis the nucleus leaves the nuclear sleeve, and 

 this sleeve with the old flagella and axostyle degenerates, new flagella 

 and new axostyles being developed by the daughter centrioles for 



Fig. G. 



1-4, Oxyvionas doroaxostyhis, from Cleveland (1950a). 1, Gametocyte, prophase, 

 nucleus still associated with extranuclear organelles, axostyle (heavy, black body), 

 flagella, and nuclear sleeve shown; 2, gametocyte, metaphase, old flagella, and nuclear 

 sleeve have disappeared, old axostyle disintegrating, each centriole producing a new 

 axostyle; 3, gametes fusing, anterior end of one joining posterior end of the other; 

 4, axostyles are fused for half or more of their length and nuclei are touching. 5, 

 6, Saccinobaciihis avibloaxostylus, from Cleveland (1950b). 5, axostyles of gametes 

 beginning to fuse bringing the pronuclei close together; 6, anaphase of zygotic 

 meiosis, old axostyles nearly disintegrated, new axostyles about half grown. 



