48 



IN VER TEBRA TE ZOOLOG Y 



Pasteur's name is closely associated with the Microsporidia 

 because of his discovery of the cause and means of control of 

 pebrine. 



The Myxosporidia have bivalve spores which usually contain 

 one, two, or four polar capsules in addition to the amoeboid body 

 called the sporo plasm (Fig. 30). The polar capsules are observa- 



Anierior end 

 ■foramen of pole 

 — Shell 



Fig. 30. 



uiural 

 ■Polar caps 

 led polar 



lef' o'fsj 

 Sporo^ 

 ■loamopf- 

 vacuo 



— Po lienor end 



-Diagrammatical front and side views of a Myxobolus spore. 



Kudo). 



{After 



ble in fresh material without previous treatment. Two nuclei 

 are found in the sporoplasm. The vegetative stage (Fig. 31) 

 occurs either as a tissue parasite or in cavities. In the cavities 

 the trophozoite forms plasmodia of various shapes. The tissue- 

 inhabiting forms are usually oval, rounded, or elongated and may 

 be either free or encysted. Spores are formed in the endoplasm 



of the plasmodial trophozoite. 

 Gall bladder, uriniferous 

 tubules, and urinary bladder 

 of fishes are common seats of 

 infection by the free organ- 

 inhabiting forms, while gills 

 and muscles of fishes are 

 especially favorable tissues for 

 the encysted forms. Cysts, 

 which may attain a diameter of 

 several millimeters, result from the hypertrophy of host tissues 

 surrounding what was originally a single parasite. By endoge- 

 nous budding of this parasite, spores in all stages of their develop- 

 ment are being produced continuously. Leptotheca, Myxidium, 

 Myxobolus, Henneguya, and Chloromyxum are characteristic 

 genera. 



Fig. 31. — Vegetative stage of a myxo- 

 sporidian, Leptotheca ohlmacheri. {After 

 Kudo) . 



