CNIDOSPORIDIA. 329 



definite intracellular stages, schizogony, and, following upon 

 conjugation of gametes, formation of oocysts within which the 

 sporozoites are formed. The Neosporidia, including the 

 Cnidosporidia, Sarcosporidia, and Haplosporidia, do not 

 form a natural group, nor have they much in common with the 

 Telosporidia. In the Neosporidia the life of an individual 

 does not come to an end when reproduction takes place, but 

 reproduction continues throughout the trophic phase, the 

 sporoblasts being carried about by the more or less active 

 organism, which may ultimately become a large mass of 

 spores. Among the Cnidosporidia the parasites may some- 

 times be intracellular, but they usually reproduce by binary 

 fission, and the zygotes do not become encysted and do not 

 produce sporozoites. The Sarcosporidia and Haplosporidia 

 possess simple spores, and do not seem to be related either to 

 the Cnidosporidia or to the Telosporidia. 



Wenyon (1926) considers it justifiable to reserve the title 

 Sporozoa for the Telosporidia, to consider the Cnidosporidia 

 as an independent class, and to regard Sarcosporidia and 

 Haplosporidia as parasites of undetermined position. 

 Reichenow (1929, 1935) regards Telosporidia, Cnido- 

 sporidia, Sarcosporidia, and Haplosporidia as independent 

 subclasses of Sporozoa. Kudo (1931) also follows this 

 arrangement, but places Sarcosporidia and Haplosporidia 

 in one subclass with the title Acnidosporidia. Calkins (1933) 

 regards Telosporidia, Cnidosporidia, and Acnidosporidia 

 as classes of the subphylum Sporozoa. 



Cnidosporidia are exclusively parasites of the Inverte- 

 brates and the lower Vertebrates, and are responsible for 

 causing epidemics of infection among animals of economic 

 importance such as fishes, silkworms, and honey-bees. There 

 are no secondary or intermediate hosts. 



Following Kudo, the Cnidosporidia are divided into four 

 orders, as follows : — 



1. Spore large; membrane bivalved ; two or [Biitschli, p. 330. 



four polar capsules visible in vivo Myxosporidia 



2. Spore large ; membrane trivalved ; three dis- [Stole, p. 346. 



tinctly visible polar capsules Actinomyxidia 



3. Spore small ; raembrane in one piece ; one [Balbiani, p. 346. 



(rarely two) polar filaments ; invisible in vivo . Microsporidia 



4. Spore small, barrel-shaped ; a thick filament 



coiled beneath the spore-membrane ; three [Kudo, p. 360. 



sporoplasms Helicosporidia 



