Transmission Experiments on the Specificity of Herpetomonas muscae-domesticae in Muscoid Flies

The large number of protozoan parasites which have been given specific names that refer to their animal hosts indicates the strong belief of parasitologists in host specificity. In many instances the results of morphological and experimental investigation have justified such a belief. The recent careful morphological studies of Simon (1922) and Hegner (1922), as well as the earlier studies of Kofoid and his co-workers, show that the species of Giardia living in man, meadow mice, rats, dogs, and rabbits are distinguishable. The feeding experiments of Simon (1922) suggest a rigid host specificity for Giardia. Failure to find animal reservoirs for human infections with Giardia, Endamoeba histolytica, and the three forms of human malaria have somewhat intensified the general belief in absolute host specificity. The workers who have investigated the flagellate parasites of the non-biting muscoid flies have, as Alexeiff (1913a) pointed out, assumed that a H.erpetomonas found in a host where it had not previously been noted is a new species. The result is that the literature contains descriptions of a large number of species of Herpetomonas which are hardly distinguishable. Alexeieff (1913b) lists as synonyms of Herpetomonas muscae-domesticae, Leptomonas drosophilae Chatton and Alilaire, L. pycnosomae Roubaud, L. ampelophilac Chatton and A. Leger, and Herpetomonas luciliae, Strickland. To his list I should add H. calliphorae Swingle, H. sarcophagae Prowazek, and H. homalonzyiae Brug. In his various writings Patton has avoided the common error by noting that Herpetomonas muscae-domesticae may be present in a number of species of hosts. Alexeieff (1913b) justified his grouping of a large number of supposed species of Herpetomonas into three species on strictly morphological grounds. He argues that, since in the protozoa we can neither apply the specific test of cross fertilization nor use the delicate cultural reactions upon which bacteriologists depend, we must use morphological criteria alone in classifying protozoa. He further makes