458 



PROTOZOOLOGY 



example. Debaisieux's observation on this myxosporidian is in 

 brief as follows (Fig. 209): sporoplasms after finding their way 

 into gall baldder of host fish develop into large trophozoites con- 

 taining many nuclei (a), 2 vegetative nuclei become surrounded 

 by a cytoplasmic mass (c) and this develops into a primary prop- 

 agative 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-i) and 2 

 sporocytes unite to form a tetranucleate pansporoblast (j) which 

 develops into 2 spores (k, I). Sporoplasm first shows 2 nuclei, but 

 later 4, of which 2 degenerate and the other 2 fuse into one nu- 

 cleus. On the other hand, according to Naville (1930) uninucleate 

 amoebula (Fig. 210, a) enters the gall bladder and develops into 

 multinucleate trophozoite in which nuclear division reveals 4 

 chromosomes (6); within the trophozoite macrogametes and mi- 

 crogametes are independently formed, during which process, 

 chromosome number is reduced into half (2) (c, d); plasogamy be- 

 tween a macrogamete and a microgamete results in production of 

 a binucleate pansporoblast (e, /), from which repeated nuclear 

 division (g-l) forms 2 spores (m); each of the 2 nuclei of the sporo- 

 plasm is haploid and the diploid number is restored when the 2 

 nuclei fuse into one (n). 



The site of infections by Myxosporidia varies among different 

 species. They have been found in almost all kinds of tissues and 

 organs of host fish, although each myxosporidian has its special 

 site of infection in one to several species of fish. The gills and gall 

 bladder are most frequently parasitized by Myxosporidia in 



Fig. 211. A channel cat, heavily infected with Henneguya 

 exilis, Xh (Kudo). 



freshwater fishes, while the gall bladder and urinary bladder of 

 marine fishes harbor one or more species of Myxosporidia. When 

 the infection is concentrated in the fins or integument, the re- 

 svdting changes are quite conspicuous (Fig. 211). The infection in 



