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THE AMERICAN NATURALIST [Vol. XLII 



mitosis into two nuclei which are separated from one another 

 by the entire diameter of the cell. The nuclei then fragment, 

 forming chromidia. while the cell becomes incompletely divided 

 into daughter cells. In some cases the entire nucleus of each 

 half disappears in the mass of chromidia granules; in other 

 cases there appears to be a secretion of the chromidial substance 

 as in Arcella, but in all cases a portion of the nuclear material 

 is thrown out of the nucleus to degenerate. From the chromidia 

 granules a new and smaller nucleus is formed in each half of the 

 cell. Each then divides by a primitive mitosis into two nuclei, 

 one of which degenerates, the other divides a second time and 

 again one of the resulting daughter nuclei degenerates. After 

 this process, which Schaudinn interprets as the equivalent of 

 reduction and polar body formation in metazoa, the final encyst- 

 ment takes place. The gelatinous membrane disappears and in 

 its place a much more refractive cyst membrane is secreted. The 

 contents of the cyst become closely united again and the two 

 remaining nuclei are brought together. Then follows a third 

 division by mitosis characterized by long connecting strands 

 which lie parallel with one another in the center of the cell and 



paired nuclei then fuse, an eighth part of one of the original 

 nuclei uniting with an eighth part of the other. Each cyst 

 thus contains two fertilized nuclei, each of which subsequently 

 divides twice to form eight nuclei. In this condition the 

 cyst passes into the intestine of a new host, where the protoplasm 

 divides into eiirht spores each with one nucleus. Wenyon's 

 account of Entamaha rnuris confirms Schaudinn "s in all essen- 

 tial features. 



While Amoeba proteus is probably far removed, phylogenet- 

 ically, from Entamoeba, there is reason to believe that the proc- 

 esses of fertilization have something in common. Four years 

 ago Calkins 3 found what he regarded as evidences of a sexual 

 phase in the life history, and described the multiplication of 

 primary nuclei and the fragmentation of these nuclei into 

 chromidia. The chromidia were interpreted as the possible 

 nuclei of future gametes, an interpretation in line with the 

 processes and outcome of chromidia formation in Foraminifera, 

 in Arcella. Centropyxis, Difflugia and other rhizopods. Subse- 



