INFUSORIA AS PARASITES. 
297 
of Amphibia which have been devoured by the water bird, and 
temporarily retained their vitality within its viscera. Pre- 
mising, however, that the position of Trypanosoma Eberthi as a 
independent organism is established, yet another problem of 
interest presents itself ; for until the entire life-histories of both 
this and T. sanguinis have been investigated, the possibility 
remains that the type found in the viscera of ducks and geese 
may represent an advanced phase only of the one inhabiting 
the blood of the Amphibia, or vice versa. A parallel association 
with two separate hosts is of common occurrence among the 
representatives of the Cestoidea and other endoparasitic worms, 
From among the group of the typical Infusoria-Flagellata, 
numerous illustrations of true parasitic existence may be cited. 
The genus Herpomonas, as recently instituted by the present 
writer, embodies two specific forms, H. muscce-domesticce and 
H. Lewisi, distinguished, as in the case of Trypanosoma , by 
their dependence on other and more highly organized animal 
types for their means of existence. Both of these species 
correspond with each other in the possession of an attenuate 
and highly flexible vermicular body, which is provided at one 
extremity with a single long locomotive flagellum. The species 
first named, Herpomonas muscce-domesticce (PI. VII. figs. 6-8), 
was originally referred by Burnet to the genus JBodo, and, as 
its specific name implies, occurs as a parasite within the 
intestinal tract of the common House-fly, not unfrequently, 
under such conditions, being present in such vast numbers as 
to almost completely fill this passage. Herpomonas Lewisi 
(PI. VII. figs. 9 and 10) is encountered under distinct and highly 
remarkable conditions. For the first, and so far only extant record 
of this species, we are indebted to Mr. H. Gr. Lewis, who discovered 
the animals as parasites of the blood in apparently entirely 
healthy Indian rats in the year 1877, and figured and described 
them, without any name, in the Quarterly Microscopical Journal , 
as simple flagellate organisms inhabiting the vital fluids of the 
above-named rodents. The specific name here associated with 
this type has been recently conferred upon it by the present 
writer in honour of its discoverer. As examined by Mr. Lewis, 
the bodies of these animalcules were found to be highly plastic 
or ‘ metabolic/ exhibiting every variety of contour, and, except- 
ing for this circumstance, corresponding to a considerable 
extent with the Ophidomonas jenensis of Ehrenberg. Ho oral 
apparatus, endoplast, or other differentiated structures, have so 
far been observed. It was ascertained that the rats infested by 
these flagellate parasites possessed an entirely local distribution, 
tenanting a restricted portion only of the premises on which 
they were discovered. A minute flagellate type presenting a 
contour closely corresponding with that of Herpomonas , but 
