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THE QUARTERLY REVIEW OF BIOLOGY 



bulletin. In the meantime the writer 

 has used the scientific and common names 

 employed in the current literature. 



The Protozoa are usually separated into 

 four classes, the members of which can be 

 distinguished by the presence or absence 

 of locomotor organs and the character 

 of these when present. The Sarcodina 

 throw out temporary cytoplasmic projec- 

 tions known as pseudopodia; the Masti- 

 gophora possess one or several threadlike 

 flagella; the Sporozoa have no locomotor 

 organs; and the Infusoria are covered more 

 or less completely with minute hair-like 

 cilia. The Sporozoa are all parasitic, but 

 the other three classes include both free- 

 living and parasitic species. Protozoa 

 are all very small; a few of them can be 

 seen with the naked eye, especially when 

 large numbers are crowded into a small 

 area, but most of them are microscopic in 

 size. Elaborate methods have been 

 evolved during the course of years for 

 their study, and it is now possible to 

 cultivate not only free-living species, but 

 also many of the parasitic forms, in test 

 tubes in artificial media. Much has 

 been learned by the use of laboratory 

 animals;, and cross-infection experiments 

 have revealed many data regarding the 

 environmental factors necessary for their 

 growth and reproduction. 



Both monkeys and man are parasitized 

 by certain members of all four classes of 

 Protozoa. For convenience we may 

 recognize two types of protozoan para- 

 sites, (i) intestinal protozoa, including 

 also those that live in the mouth, stomach, 

 vagina, and urinary tract, and (i) blood- 

 inhabiting protozoa. The former include 

 representatives among the amoebae (figs. 

 1-4), flagellates (figs. 5-9), coccidia and 

 ciliates (figs. 10-11). Many protozoa 

 have been described from human fecal 

 material that are not inhabitants of the 

 intestine but were either ingested in food 



or drink and had passed through the 

 digestive tract in a viable condition, or 

 had found their way into the feces after 

 they were passed: these are known as 

 coprozoic protozoa. The blood-inhab- 

 iting protozoa of primates consist prin- 

 cipally of certain flagellates (figs. 

 iz-13) and malarial organisms (figs. 14- 

 19). Besides the protozoa belonging to 

 the two large groups mentioned, are the 

 sarcosporidia (Sporozoa) that parasitize 

 muscle, and a few others of doubtful 

 validity. 



One of the most fascinating problems 

 in protozoology is that of host-parasite 

 specificity (Hegner, 19x6a). Why is it 

 that one species of protozoon is able to 

 live in one species of animal but not in 

 another nearly related species? This 

 appears to be true of most species of human 

 parasites. Does the ability of a protozoon 

 to live in two species of animals indicate 

 that the latter are closely related? This 

 is a problem of great interest and impor- 

 tance, since evidence of the organic evolu- 

 tion of hosts may be inferred from the 

 character of their parasites. It is mainly 

 with this point in mind that this article 

 has been prepared. A comparison is 

 presented in the following pages of the 

 amoebae, intestinal flagellates, intesti- 

 nal ciliates, trypanosomes, leishmanias, 

 malarial parasites, and certain other 

 species of protozoa that live in monkeys 

 and man. This requires the use of many 

 scientific names, both of the protozoa and 

 of their monkey hosts; but the accompany- 

 ing figures may serve to make these 

 intelligible to readers who are not biolo- 

 gists. This is followed by a brief resume 

 of the species that occur in the two types 

 of hosts, and is concluded with a state- 

 ment regarding the significance of these 

 parasites in the study of genetic relation- 

 ships of hosts as applied to monkeys and 

 man. 



