644 



PROTOZOOLOGY 



its short coiled filament, varies in number from one to four (Fig. 

 275). Except in the family Myxidiidae, in which one polar capsule 

 is situated near each of the poles of the spore, the polar capsules 

 are always grouped at one end which is ordinarily designated as the 

 anterior end of the spore. Below or between (in Myxidiidae) the 

 polar capsules, there is almost always a sporoplasm. Ordinarily a 



Fig. 275. Sporogony in Myxosoma catostomi, X2130 (Kudo), a, sporont 

 or pansporoblast; b-h, development of two sporoblasts within the spo- 

 ront; i, a nearly mature spore; j-1, views of spore. 



young spore possesses two sporoplasm nuclei which fuse into one 

 (autogamy) when the spore becomes mature. In Myxobolidae there 

 is a glycogenous substance in a vacuole which stains mahogany red 

 with iodine and is known as the iodinophilous (iodophile) vacuole. 

 The Myxosporidia are exclusive^ parasites of lower verte- 

 brates, especially fishes. Both fresh and salt water fishes have been 

 found to harbor, or to be infected by, Myxosporidia in various 

 regions of the world. A few occur in Amphibia and Reptilia, but no 

 species has been found to occur in either birds or mammals. When 

 a spore gains entrance into the digestive tract of a specific host fish, 

 the sporoplasm leaves the spore as an amoebula which penetrates 

 through the gut-epithelium and, after a period of migration, enters 

 the tissues of certain organs, where it grows into a trophozoite at the 



