Their Collection and Investigation. 47
are more especially subservient in both the erratic and
sedentary species as prehensile organs wherewith they seize
and transfer to their own bodies the protoplasmic contents
of other Infusoria. The animalcules belonging to the tenta-
culiferous class are not inferior to the Ciliata in regard to
size, and on account of their chiefly sedentary habits afford
peculiar facilities for systematic investigation.
Should the microscopical investigator be so far satisfied
with his explorations among the ciliate and tentaculiferous
classes of the Infusoria as to determine upon a like study of
the Flagellata or monadiform animalcules, he will find his
path beset by more formidable obstacles, though en revanche
he will be entering on a new and interesting field that has up
to the present time been so superficially explored that he
may look forward with almost absolute certainty to meeting
with an abundant harvest of species not yet placed on record
in the scientific annals; while in connection with an over-
whelming majority of those already known, but the scantiest
data have been registered concerning their life and develop-
mental histories. All the Flagellata are notable for their
minute size, a total length of the 1- 2- or 3-1000th parts of
an English inch being a common measurement. They con-
sequently need the higher powers of the compound micro-
scrope—a l-8th inch objective and upwards—for their satis-
factory investigation ; while even with such apparatus a
considerable amount of patience and manipulative skill is
essential for the correct definition of the number and
character of their diversely modified appendages. Up to
within a comparatively recent date the Flagellata, as a
clearly-defined animal group, could be scarcely said to exist,
its members being intermingled with the unicellular flagelli-
ferous Protophytes or lowest plants, and from which indeed
they are even yet in many instances not easily distinguished.
The application, nevertheless, of the standard that has been
selected personally as the distinction between these flagellate
Protozoa and Protophytes, namely, the capacity to ingest
solid food and the possession of a rudimentary respiratory
organ—the pulsating contractile vesicle—by the animals, and