COMMENTS ON IHl (^RICIN AND KVOI.UTION OF SEX 337 



leads to the presence of food. (5) l^'crrili/ation in its primitive sig- 

 nificance is then a phenomenon of "luirophagy." (6) This autophagy 

 has introduced into the cycle of dcxclopmcnt a new stage which 

 constitutes sexual reproduction. (7) Development of a gamete with- 

 out union with another gamete constitutes parthenogenesis. Dangeard 

 considered the haploid state the basic one. 



THE "ACCIDENTAL FUSION" THEORY 



This theory is fairly well expressed by Rhumbler (1898), who 

 made a study of shelled rhizopods (Testacea) . Referring to the close 

 similarity of the process of syngamy as described by Schaudinn 

 (1896) for Actiiiophrys sol with the sexual reproduction character- 

 istic of the Metazoa, he stated his belief that the ancestral type of 

 sexuality ^^'as to be found in the testate rhizopods. 



Rhumbler takes as a starting point the tendency of certain rhizo- 

 pods to cluster together in "nests" of individuals. He says that he has 

 seen as many as fifty individuals of Amoeba verrucosa clustered to- 

 gether but without fusions. This tendency to form clusters he calls 

 "cytotropism." 



The next step is fusion of cytoplasm, or plasmogamy, which is 

 very common among the Testacea and has been reported by a num- 

 ber of observers; and it has also been reported for other members of 

 the Sarcodina, as, for example, some heliozoans. Rhumbler states that 

 he has seen hundreds of cases of plasmogamy in Difflugia lobostoma; 

 also that during several years many pairs of different species of Dij- 

 fJiigia had been fixed and stained, but no changres in their nuclei or 

 other structures could be recognized; that is, there were no more 

 variations than occurred among single individuals. All possible com- 

 binations were seen — large nuclei, small nuclei, much reserve food, 

 little reserve food, and so on. 



Rhumbler recognized that a complete series of stages of cell 

 fusion and reduction divisions had not been established, but believed 

 that they did take place. The evolutionary steps might be: (1) cyto- 

 tropism, or the clustering of cells without fusion, caused by the 

 production of chemotactic substances; (2) "accidental" fusion of 

 cytoplasms, or plasmogamy (eventually such fusions became neces- 

 sary); (3) mixing of cytoplasms might induce nuclear divisions with 

 one daughter nucleus degenerating, thus providing for "reduction"; 



