SEX IN PROTOZOA 173 



Order Testacea 



The rendcMicy for testate rhizopods to display plasmogamy, or 

 the fusion of the cytoplasms of two or more individuals, has been 

 noted by many investigators, from the earlier observers, such as 

 Biitschli (1875) for Arcella vulgaris, Gabriel (1876) for ''Troglo- 

 dytes'" {=Chhr//iydophrys), and Leidy (1879) for Euglypha alveo- 

 lata, Arcella vulgaris, Difflugia lobostovia, and other species, down to 

 recent times. 



Biitschli (1875) saw small amoebae in the shells of two of three 

 specimens of Arcella which had their cytoplasms fused. He believed 

 that these small amoebae were offspring rather than parasites, as did 

 Hertwig (1899) and his followers, Elpatiewsky (1907), Swarczew- 

 sky (1908), and others. Swarczewsky, for example, described a life 

 cycle for Arcella vulgaris which included, besides the usual binary 

 fission, the formation of two types of amoebulae (in different indi- 

 viduals) with nuclei derived from the chromidia of the parents. These 

 were supposed to be macro- and microgametes which fused to form 

 spherical cells that developed into adults. In addition, chromidiogamy 

 was described in which the cytoplasm of two parents fused and their 

 nuclei degenerated. The chromidia were supposed to fuse or mingle 

 and then give rise to secondary nuclei which became enclosed in 

 parental protoplasm to produce a brood of amoeboid stages; these 

 developed through a Nuclearia-Yike stage to the adult condition. In 

 still other cases, after the formation of secondary nuclei out of the 

 chromidia, a process of schizogony followed which produced small 

 amoeboid individuals either without the parent emerging or after 

 the emergence of the parent. Each such "offspring" developed 

 through a Nuclearia-\ikG stage to the adult. 



Dangeard (1910) reported that he had seen no other form of 

 reproduction in Arcella besides binary fission. He stated that there 

 is only one kind of nucleus, denying that secondary nuclei formed 

 from chromidia, but he thought that uninuclearity might result from 

 nuclear fusion. Like others, he saw numerous examples of plas- 

 mogamy involving various numbers of individuals. He declared that 

 the pseudopodiospores of other authors were parasitic Nuclearia and 

 that the previously reported gamogony was the union of gametes of 

 Nuclearia that he had previously described for Nuclearia si?nplex. 



The idea that nuclei can arise from the so-called chromidia has 



