CNIDOSPORIDIA, MYXOSPORIDIA 645 



expense of the host tissue cells, and the nucleus divides repeatedly. 

 Some nuclei become surrounded by masses of dense cytoplasm 

 and become the sporonts (Fig. 275). The sporonts grow and their 

 nuclei divide several times, forming 6-18 daughter nuclei, each with 

 a small mass of cytoplasm. The number of the nuclei thus produced 

 depends upon the structure of the mature spore, and also upon 

 whether 1 or 2 spores develop in a sporont. When the sporont de- 

 velops into a single spore, it is called a monosporoblastic sporont, 

 and if two spores are formed within a sporont, which is usually the 

 case, the sporont is called disporoblastic, or pansporoblast. The 

 spore-formation begins usually in the central area of the large tro- 

 phozoite, which continues to grow. The surrounding host tissue 

 becomes degenerated or modified and forms an envelope that is 

 often large enough to be visible to the naked eye (Figs. 278, 280). 

 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 ma- 

 ture spores become set free in the water. In case the infection is con- 

 fined to internal organs, the spores will not be set free while the host 

 fish lives. Upon its death and disintegration of the body, however, 

 the liberated spores become the source 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 capable of forming pseudopodia 

 of various types. They multiply by exogenous or endogenous bud- 

 ding or plasmotomy. One to several spores are developed in the 

 trophozoite. 



Almost all observers agree in maintaining the view that the 2 

 nuclei of the sporoplasm or 2 uninucleate sporoplasms fuse into one 

 (autogamy or paedogamy), but as to the nuclear as well as cyto- 

 plasmic changes prior to, and during, spore-formation, there is a 

 diversity of opinions. For illustration, the development of Sphaero- 

 myxa sabrazesi (p. 656) as studied by two investigators may be taken 

 as an example. Debaisieux's (1924) observation is in brief as follows 

 (Fig. 276) : Sporoplasms after finding their way into the gall bladder 

 of host fish develop into large trophozoites containing many nuclei 

 (a, 6) 2 vegetative nuclei become surrounded by a cytoplasmic mass(c) 

 and this develops into a primary propagative cell (d) which divides 

 (3 chromosomes are noted) (e) and forms secondary propagative 

 cells (/). A binucleate sporocyte is formed from the latter by unequal 

 nuclear division (g-j) and 2 sporocytes unite to form a tetranucleate 



