31. _Oicomonas mutabilis_, Kent (_Oicomonadidae_), with adherent stalk.
a = nucleus.
b = contractile vacuole.
c = food-particle in food vacuole.
32, 33. _Cercomonas crassicauda_, Duj. (_Oicomonadidae_), showing two
conditions of the pseudo-podium-protruding tail.
a = nucleus.
b = contractile vacuoles.
c = mouth.]
As reserves the protoplasm may contain oil, starch, paramylum, leucosin
(a substance soluble in water, and of doubtful composition), proteid
granules. In the holophytic forms the cytoplasm contains specialized
parts of more or less definite form, known generally as "plastids" or
"chromatophores" impregnated with a lipochrome pigment, whether green
(chlorophyll), yellow or brown (diatomin or some allied pigment), or
again red (chlorophyll with phycoerythrin). In the active condition of
such coloured holophytic forms there is usually at least one anterior
"eye-spot," of a refractive globule embedded behind in a collection of
red pigment granules. The single anterior "flagellum tractellum" of so
many of the larger forms acts by the bending over of its free end in
consecutive meridians, so as to describe a hollow cone with its apex
backwards: we may imitate this by bending the head of a slender sapling
round and round while it is implanted in the soil; and the result is to
push the water backwards, or in other words to pull the body forwards,
the whole rotating on its longitudinal axis as it moves on (Y. Delage).
An anterior lateral trailing flagellum may modify this axial rotation,
and help in steering. When the animal is at rest--attached by its base
or with its body so curved as to resist onward motion--the current
produced by the tractellum will bring suspended particles up against the
protoplasm at its base of insertion. As noted by E.R. Lankester, the
posterior flagellum of many Haemoflagellates, like that of the
spermatozoon of Metazoa, propels the cell by a sculling motion behind;
he terms it a "pulsellum." Such flagellar motion is distinct from that
of cilia, which always move backwards and forwards, with a swift
downstroke and a slower recovery in the same plane; though where the
flagella are numerous they may behave in this way, and indeed flagella
agree with cilia in being mere vibratory extensions of cytoplasm.
Symmetrically placed flagella may have a symmetrical reciprocating
motion like that of cilia.
Many of the Flagellata are parasitic (some haematozoic); the majority
live in the midst of putrefying organic matter in sea and fresh waters,
but are not known to be active as agents of putrefaction. Dallinger and
Drysdale have shown that the spores of _Bodo_ and others will survive an
exposure to a higher temperature than do any known Schizomycetes
(Bacteria), viz. 250 deg. to 300 deg. Fahr., for ten minutes, although
the adults are killed at 180 deg.
The Flagellata are for the most part very minute; the Protomastigopoda
rarely exceeding 20 [mu] in length. The Euglenaceae contain the largest
species, up to 130 [mu] in length, exclusive of the flagellum.
Our classification is modified from those of Senn (in Engler and Prantl,
_Pflanzenfamilien_) and Hartog (in _Cambridge Natural History_).