24 MYCETOZOA AND RELATED ORGANISMS 



septica (L.) Gmel. and Trichia varia Pers., as well as the normal uni- 

 flagellate zoospores. Gilbert (1927) reports that in one collection of 

 Stemonitis fusca Roth he studied about one-fourth of the swarm spores 

 bore two flagella and three-fourths bore only one. Sinoto and Yuasa (1934) 

 and Yuasa (1935) showed that whether one or two flagella are produced 

 the cell is uninucleate and possesses two blepharoplasts usually connected 

 by a slender rod and joined to the nucleus by means of a single rhizoplast. 

 In the case of two flagella each blepharoplast bears one, in the case of one 

 flagellum one of the blepharoplasts remains without a flagellum, Ellison 

 (1945) confirmed Yuasa's findings and demonstrated that the flagella 

 whether single or two in number were all of the whiplash type, i.e., have 

 a firmer, outer tubular portion beyond which the interior portion projects 

 more or less or may be gathered into a ball. No flagellum of the tinsel 

 type is produced, i.e., with numerous minute cilium-like lateral out- 

 growths. Elhott (1948) made intensive studies of the germinating spores 

 of 1 1 species of this order and found that biflagellate swarm spores were 

 present in all these species, up to nearly 100 per cent in Fuligo septica (L.) 

 Gmel. In all cases except in the genus Stemonitis one flagellum is long and 

 the other very short and often somewhat recurved. Unless seen in profile 

 the shorter flagellum is difficult of demonstration. This probably accounts 

 for the earlier belief that these organisms possess but one, anteriorly 

 directed, flagellum. (Fig. 1.) 



These motile swarm cells ingest food in the manner of Amoeba, leaving 

 behind the undigested debris. This food is in many cases bacterial cells 

 but various other objects of an organic nature may be consumed. The 

 swarm cells may divide by fission several times and then change their 

 form, retracting their flagella and becoming more rounded, with usually 

 more conspicuous pseudopodia. These myxamoebae usually enlarge and 

 divide several times. Eventually they begin to unite by twos, with 

 nuclear fusion, to form zygotes. In a number of genera the myxamoebal 

 stage does not occur and the sexual fusion takes place between two swarm 

 cells {Reticularia, according to Wilson and Cadman, 1928; Didymium 

 difforme (Pers.) Duby, according to Miss Cayley, 1929; Physarum 

 polycephalum Schw., according to Howard, 1931; and others according 

 to Abe, 1934). Skupienski (1928) claims that the nuclear fusion does not 

 occur in Didymium difforme until just before spore formation. In general 

 the zygote formed by the union of two myxamoebae or of two swarm 

 cells is nonflagellate but continues its existence as a naked amoeboid cell 

 which ingests its food and grows in size, with accompanying mitotic 

 division of the nucleus. This multinucleate structure is cahed a Plas- 

 modium. Zygotes or small plusmodia may fuse with other zygotes and 

 Plasmodia so that growth is both internal and by accretion, Plasmodia 

 may ingest and feed upon swarm spores and myxamoebae. The plas- 



