PROTOZOA. 79 



of birds (p. 682). The H&mogregarince are usually harmless parasites 

 of reptiles and batrachians (frogs) ; a part of their life is passed within 

 the red cells of their host, but they have a slowly-moving stage, somewhat 

 resembling a gregarine, which occurs free in the blood. Hepatozoon 

 perniciosum is the best known of a group of haemogregarine-like parasites 

 which are parasitic, often within the white cells of the blood, in dogs, 

 in rats, and in other rodents; so far as is known, they do not cause disease. 

 The genus Babesia ( p. 686) includes parasites which cause important 

 diseases in cattle, sheep, horses and dogs. Similar parasites have been 

 found in the blood of monkeys, of dogs, of rats and other rodents. The 

 Sarcosporidia are tube-like in shape and filled with spores. They are 

 found within the cells of the voluntary muscles. The Haplosporidia 

 are an important group of very small sporozoa. Some of them are 

 parasitic in fish; one of them, Rhinosporidium kinealyi, has been found 

 in a tumor of the nose of a native of India. The Myxosporidia (p. 688) 

 are recognized by the peculiar form of their spores; each spore has a 

 capsule and is furnished with one or more threads. Members of this 

 order are parasitic in various parts of fishes and they often produce 

 disease in th*eir hosts. The spores of the Micro sporidia (p. 688) 

 are exceedingly small; a member of this order is the cause of pebrine 

 (p. 688). 



The INFUSORIA (p. 689) are a large class. Most of them are not 

 parasitic. They are the most highly developed of the protozoa and 

 their bodies are more or less covered with cilia, by which they move 

 themselves through the liquids in which they live. 



In the last class, under the heading Parasites of Uncertain Position, 

 are grouped a number of organisms which cannot be classified because 

 so little is known of them at present. Histoplasma capsulatum (p. 689), 

 the Chlamydozoa (p. 689) and the Ultramicroscopic viruses (p. 64, 690) 

 are all associated with important diseases in men and in animals. 



Those parasites which are important enough to require special 

 consideration are described in the order in which they are mentioned in 

 the classification (p. 10). Whenever it is possible to do so, a single 

 species is taken as the type of each genus and that species, with the 

 disease it produces, is described; if the remaining species of the genus 

 are mentioned, they are spoken of only to indicate how they differ from 

 the description of the type species. 



