114 PHYLUM PROTOZOA—THE SIMPLEST ANIMALS. 
also symbiotic Algee, which have lost the power of independent exist- 
ence. The evidence for this is, however, insufficient, and this explana- 
tion will not apply in cases like that of Vortzcella viridis, where the 
green colouring matter is uniformly distributed through the protoplasm. 
In many cases there is, besides the chlorophyll, a brown pigment, 
identical with the datomin of Diatoms. In many of the Flagellata 
there are one or more bright .pigment spots at the anterior end of the 
cell; these may be specially sensitive areas. In some of the simpler 
Gregarines the medullary protoplasm is coloured with pigment which is 
apparently a derivative of the hemoglobin of the host. 
Psychical life.—Protozoa often behave in a way which 
suggests control, but it should be noted that cut-off 
fragments sometimes behave just as effectively as the 
intact units. Verworn has decided, after much labour, 
that the Protozoa do not exhibit what even the most 
generous could call intelligence; but this is no reason why 
he or any other evolutionist should doubt that they have in’ 
them the indefinable rudiments of mind. Jennings has 
shown that the behaviour of some Infusorians corresponds 
to what may be called the method of trial and error; they 
“try” one kind of response after another until, in some 
cases, they give the effective answer. 
GENERAL NOTES ON THE STRUCTURE OF PROTOZOA 
The Protozoa are sometimes called “structureless,” but 
they are only so relatively. For though they have not 
stomachs, hearts, and kidneys, as Ehrenberg supposed, they 
are not like drops of white of egg. 
The cell substance consists of a living network or foam, 
in the meshes or vacuoles of which there is looser material. 
Included with the latter are granules, some of which are 
food fragments in process of digestion, or waste products in 
process of excretion. 
The cell substance includes one or more nuclei, special- 
ised bodies which are essential to the life and multiplication 
of the unit. In the Protozoa there are several conditions 
under which the nucleus may exist :— 
(1) In some adult forms, and in many spores or young forms, no 
definite nucleus has yet been discovered. It is, however, unnecessary 
to preserve the term ‘‘ Monera” for such simple forms, as it is probable 
that nuclear material does exist in the form at granules. 
