718 CLASS: CNIDOSPOKIDIA 



sporidiida, and Actinomyxidiida from the Sporozoa, with which Schaudinn 

 first grouped them, and to place them in a distinct class for which the name 

 Cnidosporidia, suggested by Dofiein (1901) for the order, can be employed. 

 The Sarcosporidia do not appear to be related either to the Sporozoa or the 

 Cnidosporidia, and will be considered with other forms with doubtful 

 affinities, as was done by Labbe (1899). 



A typical member of the class commences its existence as a small 

 amoeboid body which has escaped from the spore in the intestine of the 

 host. It makes its way to the tissue or body space in which its subsequent 

 development wdll occur. Here it may grow into a multinucleate Plas- 

 modium through repeated nuclear divisions not being followed by division 

 of the cytoplasm, or it may multiply by binary fission or possibly by 

 multiple segmentation or gemmation, so that a large number of uninucleate 

 forms is produced. In either case spore formation eventually occurs. 

 In the multinucleate plasmodial forms certain of the nuclei become 

 separated with a portion of cytoplasm as small round cells which lie in 

 vacuoles in the plasmodium. These uninucleate cells (pansporoblasts) 

 in the vacuoles then become transformed into spores, while the plasmodium 

 continues to increase in size. In the uninucleate forms the spores arise 

 from one of the uninucleate parasites (pansporoblasts). The process of 

 development of the spore from the uninucleate body with the production 

 of the polar capsules is a very complicated one, and the type of spore 

 produced in the dift'erent genera of Cnidosporidia varies considerably. 

 The ultimate infective agent within the spore is an amoeboid body which 

 has one or two nuclei. It has often been referred to as a sporozoite, but 

 there is no evidence that it is homologous with the typical sporozoites of 

 Sporozoa, The Cnidosporidia include three orders: Myxosporidiida, 

 MiCROSPORiDiiDA, and Actinomyxidiida. 



A. Order: MYXOSPORIDIIDA. 



In these forms the trophic or growing phase is a multinucleate 

 plasmodium, which resembles an amoeba in that it is motile and forms 

 pseudopodia (Fig. 304). They are typically parasites of cold-blooded 

 vertebrates, a large number of species infecting fish, amongst which they 

 give rise to severe and fatal epidemics. In some cases they live as 

 harmless amoeboid organisms in the body spaces, such as the gall bladder, 

 urinary bladder, or tubules of the kidney, where they float about or are 

 attached to the walls by pseudopodia. It is in these forms that the 

 complicated process of spore formation has been chiefly studied. In other 

 cases they are definite tissue parasites, which may give rise to nodules, 

 sometimes of large size, on the skin and gills or in the muscles and 

 other organs (Fig. 305). In the tissues the parasite may grow actually 



