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accepting only free lodging, and it may be the means of transit, 
at the hands of their co-sociates. 
It is proposed in the present instance to direct attention 
only to the consideration of the innumerable forms of Infusoria 
which are referable to the category of ‘ Parasites ’ in the strictest 
and simplest sense, postponing, possibly, to a future occasion 
an account of those that lead a commensal life. It will be found 
most convenient to examine these parasitic types in association 
successively with the three primary classes of the Flagellata, 
Ciliata, and Tentaculifera, commencing with the first-named or 
lowest in the organic scale. 
The Flagellata, but recently recognized as forming a clearly 
delimited and natural group of the Infusoria, are found to ex- 
hibit several very important modifications with relation more 
especially to their oral or inceptive systems and the character 
of their locomotive appendages, these furnishing indeed the 
basis upon which the present writer has established the various, 
and mostly newly introduced, orders of the class, embodied in 
a treatise devoted to an account of all known Infusorial 
organisms, now in course of publication.* The lowermost term 
in this series, as represented by the order of the Trypano- 
somata, is remarkable for containing two species only, Trypano- 
soma sanguinis and T. Eberthi , both notable for their essentially 
parasitic habits. The first of these, as represented in PI. VII. 
Figs. 1 and 2, occurs abundantly in the blood of Frogs and other 
Amphibia ; whilst the second, PL VII. Fig. 3-5, has been 
obtained as a parasite of the intestinal viscera of ducks and 
geese. High interest is attached to both of these, inasmuch as 
they represent the Flagelliferous series of the Infusoria in its 
most rudimentary condition. In neither instance is a flagellum 
distinctly developed, but in T. sanguinis one extremity is produced 
in a tag-like manner, and by the movements of this, combined 
with the undulations of the thinner lateral margin of its com- 
pressed body, it makes rapid progress through the fluid medium 
it inhabits. In T. Eberthi there is no tag-like anterior 
prolongation, the lateral margin being, however, developed as 
a still more conspicuous undulating, frill-like border. It is 
a remarkable fact that the contour of this last-named type 
corresponds to a very considerable extent with that exhibited 
by the spermatozoa of certain Amphibia, and more especially 
with those of Bombinator igneus, as originally figured by 
Leuckart and Siebold. This circumstance not unnaturally 
leaves grounds for some slight shadow of doubt as to whether 
this reputed species can be justly regarded as an independent 
form, or whether it does not represent the spermatic elements 
* A Manual of the Infusoria, by W. Saville Kent, F.L.S., F.R.M.S. 
Part I. October, 1880. liavid Bogue, 3 St. Martin’s Place. 
