SEXUAL PHENOMENA IN THE PROTOZOA 237 



twenty or more primary cysts. Each primary cyst is surrounded by a 

 special gelatinous mantle ; the nucleus of each divides once (primary 

 mitosis) into two nuclei characterized by radiations at one pole, where 

 a centrosome is developed from nuclear threads which grow out into 

 the surrounding cytoplasm. During the formation of the centrosome, 

 the body of the primary cyst divides, giving rise to the secondary 

 and mononucleate cysts. 



Each secondary cyst forms two " polar bodies " in the following 

 manner. In each the nucleus divides by mitosis into two nuclei, one 

 of which degenerates while the other prepares for a second division by 

 mitosis. After this division one of the resulting nuclei also degener- 

 ates ( " 2d polar body " ), leaving one ripe nucleus in each secondary 

 cyst. Both polar bodies consist exclusively of nuclear matter, and they 

 rapidly degenerate. Both polar or maturation mitoses are character- 

 ized by the presence of centrosomes derived from the original centre. 

 After the two secondary cysts formed from the two primary cysts are 

 ripe, they fuse together, protoplasm with protoplasm, and nucleus with 

 nucleus, thus re-forming the primary cyst. The fusion product (germ- 

 sphere) is distinguished from the older primary cyst, not only in the 

 changes described in ripening and fertilization, which, after the forma- 

 tion of the polar bodies, would hardly be noticed, but in the following- 

 additional points : (i) The body concentrates into a denser structure 

 and smaller circumference. (2) The last remnants of vacuoles disap- 

 pear. (3) The silicious particles at first diffuse, collect at the periphery 

 and finally form a compact outer coating. (4) A protective mem- 

 brane (yolk membrane), extremely impervious to killing agents, is 

 secreted inside of the protective coating. After a week's rest the 

 germ spheres creep out, each animal holding six or eight nuclei, 

 formed by mitosis. Before beginning to grow, the spheres appar- 

 ently divide into mononucleate forms. 



Again in Adelea ovatd, one of the Coccidiida, a somewhat similar 

 elimination takes place, but in only one of the conjugants. Prior to 

 conjugation, the nucleus of the male cell divides twice, and only one of 

 the resulting nuclei penetrates and fertilizes the egg, while the other 

 three disintegrate and disappear (Schaudinn and Siedlecki, '97). This 

 case is very similar to the well-known maturation-divisions among the 

 Infusoria, although in the latter both conjugants undergo the same 

 processes. In the different species of Infusoria the maturation-phe- 

 nomena, while differing as to. details, agree in their essential features, 

 and for purposes of illustration Paramcecium caudatum may be 

 selected, for with its single macronucleus and single micronucleus it 

 is simpler than the majority of other forms. The details of the pro- 

 cess which have been made out by Maupas ('88, '89) and Hertwig ('89) 

 are as follows. The micronucleus of each conjugant divides twice to 



