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HANDBOOK OF PROTOZOOLOGY 



produced depends upon the structure of the mature spore, and 

 also upon whether one or two spores are developed in a sporont. 

 When the sporont develops into a single spore, it is called a 

 monosporoblastic sporont. If two spores are formed within a 

 sporont, which is usually the case, the sporont is called disporo- 

 blastic, or pansporoblast. The spore-formation begins usually in 

 the central area of the large trophozoite, which continues to 

 grow. The surrounding host tissue becomes degenerated or 

 modified and forms an envelope which is often large enough to 

 be visible to the naked eye. This is ordinarily referred to as a 

 myxosporidian cyst. If the site of infection is near the body 

 surface, the large cyst breaks and the mature spores become set 

 free in the water. In case the infection is confined to internal 



Fig. 128 Stages in spore-formation of Myxosoma catostomi. Y.llS (After 



Kudo), 

 a, sporont; b-j, developmental stages of spores; k, 1, two views of stained 

 spores; m, n, o, front, end, and side views of preserved, unstained spores. 



organs, the spores will not be set free while the host fish lives. 

 Upon its death and distintegration of the body, however, the 

 liberated spores become the sources of new infection. 



The more primitive Myxosporidia are coelozoic in the host's 

 organs, such as the gall bladder, uriniferous tubules of the 

 kidney, urinary bladder, etc. In these forms, the liberated 

 amoebulae make their way into the specific organ and there 

 grow into multinucleate amoeboid trophozoites which are capa- 

 ble of forming pseudopodia of various types. They multiply by 

 exogenous or endogenous budding or plasmotomy. One to 

 several spores are developed in the trophozoite. 



The site of infections by Myxosporidia varies among dif- 

 ferent species. They have been found in almost all kinds of 

 tissues and organs of host fish, although each myxosporidian 



