328 RESEARCH IN PROTOZOOLOGY 



to occur, the great majority of the spore of one and the same 

 species are somewhat uniform in form with Httle variation. 



The size of the microsporidian spores also varies a great deal 

 between wide extremes (1.25 by ifi in Nosema pulvis and 17-23 

 by 3-5/1 in Mrazckia argoisi), but the majority are less than ten 

 microns in length. 



In almost all cases, the mature spores of one and the same 

 species occurring in a single host cell or tissue appear to vary 

 in size to some extent. One, however, finds intermediate forms 

 between the two extremes. Perhaps the most striking examples are 

 found in Nosema marionis (1.5-7// ^oi'^&)» Steinpellia mutabilis 

 (2-6// long), S. magna (12. 5-16.5// long), etc. A somewhat 

 regular dimorphism has been noted by several investigators, while 

 others hold that such a state does not exist. 



The spore is covered by a spore membrane and contains a 

 sporoplasm and a polar filament. The spore membrane is fairly 

 refractive, and ordinarily of a uniform thickness. Its outer sur- 

 face is smooth and structureless. In three species (Thelohania 

 giardi, Gurleya tetraspora and Mrazckia piscicola, Cepede, 1924), 

 fine longitudinal striae were noted. Unlike myxosporidia, the spores 

 of MICROSPORIA rarely bear appendages, only four species being 

 known to possess any {Mra^ekia candata, M. hrevicauda, M. 

 piscicola and Thelohania octosppra). Because of the minuteness of 

 the majority of spores, it is a matter of dispute whether the spore- 

 membrane is composed of two valves, as in myxosporidian spores, 

 or of a single piece. In the great majority of species, it appears to 

 be a single piece, while in a few species the bivalve nature of the 

 membrane has been established. Little is known concerning the 

 chemical nature of the spore membrane. The spore membrane of 

 Nosema bombycis and A^. apis was found to be composed of 

 chitinoid substance. 



The structure of the microsporidian spore has been, and still is, 

 disputed, which is without doubt due to the minuteness of the 

 object, to the peculiar nature of the spore membrane, to the present 

 state of optical apparatus and microscopic technique and to the 

 probable dissimilarity of structure among different species. 



When viewed in the fresh condition, the microsporidian spore 

 may show either a distinct vacuole or clear space at one end (as in 

 Nosema cyclopis, etc.) or two large vacuoles, one at each end (as 

 in the species of Glugea). In larger spores, the filament may be 



