SIX ix PRoro/oA 179 



sonic examples of rlic lirsr of these di\ isions the prophase and nicta- 

 phasc chromosomes had rhe appearance of tetrads. Foyn stated that 

 the number of cliromosomes varied between ten and twenty, but the 

 drawings showino- the tetrads lia\ e the smaller numbers. Although 

 Foyn suggests tiiat these appearances, which resemble meiotic divi- 

 sions, may be the result of fixation, it is possible rliat a true meiosis 

 is indicated as claimed by Le Calvez (1946, 1950). 



Le Calvez (1946), in new studies of Discorbis vilardeboaua with 

 flagellated gametes and of rateUina corniircita with amoeboid gam- 

 etes, declared that chromosome reduction rakes place during the last 

 two nuclear divisions preceding the formation of gamonts by mul- 

 tiple fission (schizogony), the entire gamont generation, therefore, 

 being haploid. In a still more recent paper, Le Calvez (1950) reiter- 

 ated his conclusions about ratelliva cornigata and Discorhis vilarde- 

 boana and added a study of association of gamonts of Discorbis iiicdi- 

 terraiieiisis. In the last species association takes place among gamonts 

 derived from a single microspheric "schizont" (agamont). Tw^o sex- 

 ual tendencies wxre evenly distributed among the gamonts, and Le 

 Calvez believed that chromosome reduction played a decisive role 

 in determining this sexual segregation. He believed that gamonts pro- 

 duce chemical attractants which bring together the gamonts of oppo- 

 site sex which are morphologically indistinguishable. Some kinds of 

 Foraminifera, he stated, like Discorbis orbicidaris and Entosolemis 

 Tnar<jriiiata show^ only a succession of mononucleate generations which 

 may be regarded as haploid parthenogamonts. If attractants are pro- 

 duced by these animals, they appear at two stages, one to bring 

 gamonts together, and the other to attract the gametes together. 



Order Heliozoa 



Sexual reproduction seems to be well established for a few species 

 of Heliozoa. Cell fusion, or plastogamy, is a fairly common phenome- 



FiG. P. Syngamy in Actiiwphrys sol, from Kuhn (1926) after Belaf (1923), 



redrawn. 



1, mitotic division of an individual with temporary cyst membrane; 2, two game- 

 tocytes resulting from this division, "bouquet" stage of nuclei; 3, early tetrad stage, 

 left (male) individual slightly more advanced than right (female); 4, first meiotic 

 division; 5, second meiotic division, first "polar bodies" above; 6, initiation of fertili- 

 zation by pseudopodial formation by male (left); 7, fusion of nuclei in zygote; 8, 

 encystment of zygote. 



