174 SEX IN MICROORGANISMS 



largely been abandoned in recent times. The presence of small amoe- 

 bae in the shells of Arcella is not too uncommon (I have observed 

 them myself), but there seems to be no real evidence that they have 

 any part in the life cycle of Arcella. Definite evidence of syngamy in 

 this genus appears to be lacking. 



Plasmogamy has been reported for certain other members of the 

 Arcelhdae. Although Gabriel (1876) and Schaudinn (1903) reported 

 cell fusion in Chlmnydophrys stercorea, the well-known process of 

 budding and colony formation in this species might be misinterpreted. 

 Martin (1912) cultivated this species for a year without seeing any 

 signs of sexuality. However, Belaf (1921) reported plasmogamy for 

 Chlamydophrys minor and C. scbaudinni, which included nuclear 

 fusion, but he stated that karyogamy resulted in death of the cells. 



Penard (1902) merely mentions finding a pair of individuals 

 of Fyxidicula cyinbahmi in "conjugation," as did also Cash and 

 Hopkinson (1909) for Cryptodiffliigia ovi^ormis. However, Ivanic 

 (1935a) reported complete "copulation," including nuclear fusion, 

 for CochUopodhiin digitatiivt. "Copulae" with food reserves were 

 able to undergo further development, but those without such reserves 

 could not. After a rest period, during which the food reserves were 

 used up, each "copula" divided into two cells in the parent shell. 

 These emerged in amoeboid form and each produced a new shell. 



Plasmogamy, or the fusion of cytoplasms, has frequently been 

 reported for species of Difflugia, for example by Leidy (1879), 

 JickeH (1884), Verworn (1888, 1890), Rhumbler (1898), Penard 

 (1902), Zuelzer (1904), Cash and Hopkinson (1905), Edmondson 

 (1906), Goette (1916), PatefT (1926) and Dangeard (1937). In some 

 cases the contents of one shell migrated into the other one, after 

 which nuclear fusion might occur (Dangeard), but usually was not 

 observed (Rhumbler). 



Rhumbler (1898) stated that he had seen hundreds of cases of 

 plasmogamy in Difflngia lobostovia, sometimes involving three indi- 

 viduals and occasionally four. During the previous several years he 

 had stained many pairs but found no unusual nuclear conditions. On 

 the other hand, Zuelzer (1904) reported not only plasmogamy in the 

 multinucleate D. iirceolata, which had nothing to do with reproduc- 

 tion, but also "copulation" and "conjugation." Plasmogamy lasted 

 for as short a time as 2 hours, but more often for 2 or 3 days, and 

 exceptionally for 8 to 14 days. Plasmogamy seemed to be more fre- 



