56 



Reproduction and Life-Cycles 



of the body and then shared between the daughter organisms in transverse 

 fission (238). Blepharoplasts, basal granules, kinetoplasts, and sometimes 

 chromatophores and pyrenoids, are self-reproducing. Their duplication 

 during fission fills the needs of the daughter organisms. Other structures, 

 including the cirri of certain ciliates and the parabasal apparatus of cer- 

 tain flagellates, undergo resorption so that each daughter organism must 

 develop a set of its own — in the case of cirri, apparently by outgrowth 

 from inherited basal granules. The resorption of parental structures is 

 sometimes extensive. Reproduction may thus involve dedifferentiation of 

 the old body as well as the differentiation of new structures in the de- 

 veloping daughter organisms. The beginning of differentiation, in two 

 new centers of organization within the parental body, possibly supplies 

 the stimulus for subsequent dedifferentiation. 



Reproduction of multinucleate Protozoa, or of multinucleate stages in 

 the life-cycle, may involve either budding or fission. In many Sporozoa a 

 young uninucleate stage grows, with repeated mitoses, into a multinu- 

 cleate Plasmodium (Fig. 2. 1, A) which then reproduces by schizogony. 

 Essentially, schizogony is multiple budding in which separation of uni- 

 nucleate buds from a residual mass of protoplasm is completed within a 

 short time (Fig. 2. 1, B). Certain multinucleate Protozoa normally divide 

 into several organisms, each of which receives some of the parental nuclei. 

 This process, not necessarily synchronized with nuclear division, is known 

 as plasmotomy. Both schizogony and plasmotomy have been described 

 in Coelosporidmrn (119), while plasmotomy is characteristic of Pelomyxa 

 (158). In the latter (Fig. 2. 1, C, D), plasmotomy produces 2-6 smaller 

 organisms, among which the parental nuclei are distributed at random. 

 Less variation is characteristic of Coronyinpha octonnria (151), in which 

 all eight nuclei usually undergo mitosis and the daughter nuclei separate 

 in groups of eight before plasmotomy occurs (Fig. 2. 1, E, F). 



Binary fission 



In Mastigophora, fission may occur in the active stage, within 

 a cyst, or in non-flagellated palmella stages (Fig. 2. 2, K). The plane 

 of fission is most frequently longitudinal and the division-furrow usually 

 appears first at the anterior end (Fig. 2. 2, I). Among the dinoflagellates, 

 however, fission is often oblique and may be almost transverse in late 

 stages (Fig. 2. 2, A-H). Spirotrichonympha bispira divides transversely, 

 although related species undergo longitudinal fission (61). Mitosis in 

 Trichomonadida is commonly followed by migration of the karyomasti- 

 gonts to opposite sides of the body and fission is then completed by cyto- 

 plasmic constriction (Fig. 2. 2, J). 



Cytoplasmic structures^ may undergo division, resorption followed by 

 origin de novo, or partial resorption followed by growth and differentia- 



^ The literature on several groups of flagellates has been reviewed by Kirby (152). 



