sponges, the microscope reveals certain elements 
called cells, which serve as a foundation for the 
structure; but we do not find even this in the Pro- 
tozoa. They are merely independent and freely- 
moving cells, and consist of protoplasm, a slimy 
jelly-like substance, which is recognised as organic, | 
and which also exists in the cells of the highest 
animals. But there is no structure in the protoplasm 
of the Protozoa, and it concentrates in itself all the 
functions which are assigned to separate organs or 
systems of organs in the higher animals. The sim- 
plicity of the Protozoa is sometimes varied by the 
relationship which the organic mass exhibits towards 
inorganic matter. We have already seen in other 
groups of animals, such as the Holothurie, the 
corals, and sponges, how inorganic matter such as 
lime or silex enters largely into the structure of the 
body in many animals; and this occurs likewise in 
Class. I. 
Plate XXII 
It was formerly supposed that these microscopic 
organisms were produced by steeping dry  sub- 
stances in fluids, but we now know that the germs are 
carried about by any puff of wind, and can thus 
reach any fluid, however well preserved, and revive. 
The Infusoria are the highest Protozoa, for their 
protoplasmic body is enclosed in a thin integument 
of determinate form, and is often provided with 
cilia in certain situations. The protoplasm contains 
darker spots or nuclei, as well as a clear bladder 
which contracts at regular intervals. 
Reproduction takes place as follows: Two indi- 
viduals fuse themselves together, and the new animal 
grows to a certain size, and then divides in two, 
and these continue to subdivide until they have 
reached the size at which they combine with another 
individual. The Infusoria feed on smaller examples 
of their own Order, or on the microscopic larve of 
higher animals; or live as parasites in the intestines 
or other organs of various animals. 
Fig. q. Opercularia nutans and fig. r. Vorticella 
microstoma are among the prettiest fresh-water species, 
and are common in streams and ponds. Both rest 
on stalks, and the mouth, at the end of the pitcher- 
shaped animal, is surrounded by a ring of constantly 

. (right side) 

the Protozoa. Many species possess acalcareous or 
siliceous skeleton of determinate form Thus arises 
a wonderful richness of genera and species among 
the Protozoa, which all exhibit the same protoplasmic 
structure to our perceptions, though their varied and 
delicate skeletons are the microscopist’s delight. The 
Protozoa are likewise of great geological importance, 
for their microscopic shells, heaped together in untold 
millions, formed vast masses of former 
ages, which have since been upheaved, forming a 
thick layer which covers thousands of square miles 
in many parts of the world. The Infusoria are nu- 
merous both in fresh water and in the sea, and their 
germs are found everywhere. Many species may 
be dried up, and revived under more favourable con- 
ditions, and are thus able to withstand all normal 
variations of heat and moisture. 
rock in 
Infusoria. 
vibrating cilia. (The names of the plate should be 
corrected as above). The Bell-Animalculae are con- 
stantly oscillating backwards and forwards, and at 
the least touch the stalk of Vortcced/a rolls itself instan- 
taneously into a spiral. 
Fig.s. Stylonichia mytilus isa freely swimming 
Infusorium provided with a number of shorter or 
longer bristles. When a drop of water in which Alga 
grow is placed under the microscope, this animal 
will generally be seen in constant movement, some- 
times darting straight onwards, and sometimes re- 
volving on its own axis between the fronds of the 
Alge. 
Fig. t. Noctiluca miliaris is a marine form. 
It is found gregariously in many places, and when 
the conditions are favourable it rises to the surface 
in such multitudes that the sea becomes slimy, and 
emits a reddish light over a wide area. After sunset, 
and especially in the early morning hours, the whole 
surface shines with a magical bluish light. The 
luminority of the sea is due in great part to the 
presence of this little infusorium, though other and 
larger luminous animals are also present. This is, 
however, a phenomenon which is only seen at its 
best at uncertain intervals. 
Class II. Rhizopoda. 
These are animals without determinate form, 
and destitute of cilia. The skinless protoplasm throws 
out and retracts processes from any part of the body 
indifferently. Thus the animal changes its shape con- 
tinually, and these processes, or pseudopodia, serve 
both to effect the movements of the animal, and to 
take food, as they surround and absorb any organic 
substances, such as Alge. Although the proto- 
plasmic body itself is of no determinate shape, 
yet it is frequently accompanied by calcareous or 
siliceous skeletons of various fixed shapes. 
Order I. Radiolaria. 
The Radiolaria always possess a siliceous ske- | 
_leton, consisting either of variously-formed needles 
which unite in the midst of the protoplasmic mass, | 

from which they radiate in different directions; or of 
a connected skeleton variable in form, with numerous 
openings through which the central protoplasmic body, 
