112, PHYLUM PROTOZOA—THE SIMPLEST ANIMALS. 
group. In many of the Hzemosporidia 1 part of the life cycle takes 
place in an intermediate host, usually a mosquito or a tick. 
Other groups of the Sporozoa are the Myxosporidia, with peculiar 
nematocyst-like organs (Invertebrates and cold-blooded Vertebrates), 
and the Sarcosporidia, which are found inside the striped muscles of 
warm-blooded Vertebrates. 
GENERAL NOTES ON THE FUNCTIONS OF PROTOZOA 
Movement.—The simplest form of movement is that 
termed amceboid, as illustrated by an Amada. In ordinary 
conditions it is continually changing its shape, putting forth 
blunt lobes and drawing others in. With this is usually 
associated a streaming movement of the granules. A more 
defined contraction, like that of a muscle cell, is illustrated 
in the contractile filament of the stalk of Vortzce//a and similar 
Infusorians ; and not less definite are the movements of cilia 
and flagella, by means of which most Infusorians travel 
swiftly through the water. Cilia in movement are bent and 
straightened alternately ; while flagella, which are usually 
single mobile threads, exhibit lashing movements to and fro, 
or, more often, are held stretched out in front, and by a 
curious rotatory movement draw the cell along. They are 
then more aptly termed ¢vacte//a. It seems probable that 
cilia and flagella consist of an elastic core surrounded by 
a sheath, which may be uniformly contractile, or may have 
one contractile band, or two opposite contractile bands, and 
so on. 
Considered generally, the movements are of two kinds: either (1) re- 
flex, z.e. responses to external stimulus, as when the Protozoon moves 
towards a nutritive substance ; or (2) automatic, z.e. such movements as 
appear to originate from within, without our being able to point to the 
immediate stimulus, e.g. the rhythmical pulsations of contractile 
vacuoles. Actively moving Protozoa usually show the following motor 
reaction to stimulus:—they move backward, turn over on one side 
structurally defined, and then move forward again. 
Sensitiveness.—The Amceba is sensitive to external influ- 
ences, It shrinks from strong light and obnoxious materials ; 
it moves towards nutritive substances. This sensitiveness 
is, so far as we know, diffuse—a property of the whole of 
the cell substance; but the pigment spots of some forms 
are specialised regions. 
