PROTOZOA 139 



vertebrate animals. They are a very important order. The genus 

 Plasmodium causes malaria in man (page 890) ; while Proteosoma and 

 H&moproteus are malarial parasites of birds (page 890) . The Hcemogre- 

 garina 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 gregar- 

 ine, which occurs free in the blood. Hepatozob'n 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 (page 894) 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. TheHaplosporidia 

 are a group of very small sporozoa of which little is known. Some of 

 them are parasitic in fish; one of them, Rhino sporidium kinealyi, has 

 been found in a tumor of the nose of a native of India. The Myxo- 

 sporidia (page 899) are recognized by the peculiar form of their spores; 

 each spore has one or more capsules each furnished with a coiled fila- 

 ment or thread which is extruded under certain conditions and probably 

 serves to anchor the spore to a surface upon which further development 

 may occur. Members of this order are parasitic in various tissues of 

 fishes and they often produce disease in their hosts. The spores of the 

 Microsporidia (page 899) are exceedingly small; a member of this 

 order is the cause of pebrine in silk- worms (page 937). 



The INFUSORIA (page 899) 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. 



Lastly, 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. The spirochaetiform organisms, 

 Histoplasma capsulatum (page 900), the Chlamydozoa (page 900), the 

 Rickettsias, and the Ultramicroscopic viruses (page 119) are all asso- 

 ciated with important diseases in men and in animals. 



The SPIROCH^T^E (page 900), as their name signifies, are thread-like 

 organisms, which seem to be coiled in a spiral. It is probable that the 



