Sporozoa 323 



Fig. 6. 33. Helicosporidium parasitkum; A-H, x3720; I, x2325; J, xl400 

 (after Keilin): A. Young growth stage. B. Binucleate growth stage. C. Four- 

 cell stage. D. Eight-cell stage. EG. Stages in development of the spore; a 

 young spore with a central mass surrounded by a protoplasmic rim (E); 

 lateral and end views of a later stage with three central cells, spiral filament 

 not yet differentiated (F, G). H. Mature spore showing peripheral spiral 

 filament and the three central cells. I. Spore membrane ruptured and spiral 

 filament protruding. J. Unravelled filament after rupture of the spore mem- 

 brane; these filaments are 60-65,u long and contain one nucleus. 



four cells. One of the four is believed to spread over the others to form 

 a capsule (Fig. 6. 33, E-G). A spiral filament develops later but its exact 

 origin is unknown. The mature spore (Fig. 6. 33, H) contains three cells 

 ("sporozoites"), supposedly infective stages, and the spiral filament, be- 

 lieved to play the role of an elater when the membrane is ruptured. When 

 spores are placed in water the spore membrane is ruptured, the filament 

 is extruded (Fig. 6. 33, I, J), and the three central cells are expelled. 



CLASS 3. ACNIDOSPORIDEA 



The organisms usually assigned to this class do not produce spores 

 containing polar filaments and are thus unlike the Cnidosporidea. Their 

 life-cycles fail to suggest any close relationship to the Telosporidea. Fur- 

 thermore, the interrelationships of the groups included in the Acnido- 

 sporidea are somewhat obscure, and as now constituted, the class may be 

 largely a taxonomic convenience. As a result, the conventional division 

 of the Acnidosporidea into the Subclasses Sarcosporidia and Haplospo- 

 ridia indicates no firm belief that the two groups are as closely related 

 as this arrangement might imply. 



