PHYLUM PROTOZOA IN GENERAL 73 



cated. There are three subclasses of the class, and each of these is 

 divided into some orders. The first subclass is Telosporidia in which 

 the spores produced have neither a polar capsule nor polar filament. 

 In this group are three orders, (a) Gregarinida (Fig. 29), commonly 

 called gregarines, inhabit the cells (cystozoic) of earthworms, cock- 

 roaches, other insects, and occasionally vertebrates in their early 

 stages, but later they may become free in the cavities of the host. They 

 may attain considerable size, (b) Coccidia are minute monocysted 

 forms which are permanent intracellular parasites of molluscs, arthro- 

 pods, and vertebrates, including man. The life history involves a 

 period of asexual reproduction (schizogony) and a period of so-called 

 sexual reproduction which ends in spore formation (sporogony). (c) 

 Haemosporidia. The representatives of this order live chiefly in the 

 red blood corpuscles of vertebrates. Again the life cycle involves 

 both schizogony and sporogony. The former occurs in the blood of 

 the vertebrate and the latter takes place in such hosts as insects, 

 leeches, and ticks. The malaria parasite and the causal agent of 

 Texas fever in cattle are the most important forms, 



Cnidosporidia is the name of a second subclass, the spores of which 

 contain from one to four polar capsules each with a coiled polar fila- 

 ment. There are two orders : (a) Myxosporidia are found chiefly as 

 fish parasites, but occur occasionally in reptiles and amphibia. The 

 gall-bladder, uriniferous tubes, and urinary bladder are usual seats 

 of infection for the free forms, while the gills and muscles of the 

 fishes are choice tissues for the cysts. Myxidium and myxoholus are 

 characteristic genera, (b) Microsporidia have in each spore a single 

 polar capsule. This group is parasitic chiefly in arthropods, and 

 occasionally in other invertebrates, fish and amphibia. 



The third subclass Acnidosporidia includes forms which produce 

 simple spores. Again there are two orders: (a) Sarcosporidia. As 

 the name infers these occur in muscles of several mammals. The 

 encysted forms attain a length of several millimeters, and ultimately 

 each becomes a mass of sickle-shaped spores. The complete life cycle 

 is not known, but the saclike, encysted form in muscles of mammals 

 is known as Miescher's tube or sac. (b) Haplosporidia are single cells, 

 each with a single nucleus, and they have a relatively simple struc- 

 ture. This order parasitizes fishes and certain insects, notably the 

 cockroach. 



