SEX IN PROTOZOA 135 



CLASS MASTIGOPHORA 



Kudo divides the Mastigophora into two subclasses, the Phy- 

 toniasrigina, or plant flagellates, and the Zoomastigina, or animal 

 flagellates. The Phytomastigina include the orders Chrysomonadina, 

 Cryptonionadina, Phytomonadina, Euglenoidina, Chloromonadina, 

 and Dinoflagellata. The books by Fritsch (1935) and Smith (1950, 

 1951a), are useful in connection with this group. 



Order Cbry soiiionadina 



Evidence for sexual reproduction in this group is scanty and 

 incomplete. Schiller (1925) saw sixteen small cells inside a mother 

 shell of Calyptrosphaera sphaeroidea (Coccolithophoridae) and 

 thought they might be gametes, but recorded no cell fusions. The 

 same author (1926) reported fusion of isogametes produced by 

 division of the protoplast of Dinobryoii sertularia. The zygotes lost 

 their flagella and sank to the bottom, but no further development 

 was observed. Krieger (1930) noted that cysts of Dinobryon cyl'w- 

 dricwn and of D. divergens were binucleate. This was confirmed by 

 Geitler (1935), who also observed cyst formation. The nucleus 

 divided (without reduction) before the cyst walls were developed. 

 Germination of the cysts was not seen, but Geitler supposed that 

 the two sister nuclei united before germination, thus accomplishing 

 autogamy. Schwarz (1932) described gamete formation, syngamy, 

 postzygotic meiosis, and development of four new cells from the 

 zygote in Ochrosphaera neapolitana (Fig. A, 1 to 12), Lackey (1938) 

 occasionally found a globule of protoplasm between two loricae of 

 Chrysococcus spiralis (13) and less often for C. heinisphaerica, which 

 he thought might possibly indicate "conjugation." Skuja (1950) 

 reported isogamy with encystment of the zygote in Dinobryoii 

 borgei, and Mack (1951) found encysted zygotes with adhering 

 loricae of the uniting individuals in Chrysolykos planktonicus (15). 



While there are thus strong indications of isogamy in this group 

 of flagellates, full details of the life histories and chromosome condi- 

 tions are not provided in any of the descriptions except that for 

 Ochrosphaera 7ieapolitana. 



