Trotozoa. KADIATA. Infusoria. 403 
few species, and .these are all natives of fresh water. 
longing to it possessing, when adult, a locomotive 
The animals have their tentacles disposed in a crescentic 
faculty. This creature is a native of the fresh waters 
or horse- shoe series round the disc surrounding the 
of Great Britain, and is found floating on the surface. 
mouth. The order is well represented by the “ Bell- 
Though it does possess motion, its progression is very 
flower Animals” of some of the earlier writers on the 
slow, seldom exceeding an inch in twelve or twenty- 
microscope, the genus Plumatdla. Another genus, 
four hours. This beautiful species forms a fine object 
Cristatella, is remarkable from the only species be- 
for microscopic inspectioa 
Class IV. — 
PROTOZOA. 
The Class Protozoa, contains an immense number of 
in high latitudes, where vegetable life ceases to be 
creatures, very minute in size, and very low in organi- 
represented, but where animal life is still in abundance. 
zation. They all belong to two large orders — 1. In- 
Infusoria are there found to exist in inconceivable 
fusoria; 2. Rhizopoda. 
numbers, and form the principal food of the fishes 
inhabiting these regions. They frequently occur in 
Order I. — INFUSOEIA (Infusory Animalcules). 
such immense numbers as to colour large tracts of 
water with very remarkable hues. Some species im- 
The animals belonging to this order of animals are 
part a hlood-red tint to the water, and Ehrenberg has 
for the most part extremely minute, and have been 
thrown out the conjecture that these little creatures 
made known to us by the aid of the microscope. They 
were the agents employed in the miracle worked by 
inhabit stagnant water, fresh or salt, in which plants 
Moses in turning the waters of Egypt into blood ! 
are growing, or in which an abundance of decayed 
Others give a blue colour, while a third set tinge the 
vegetable or animal matter is contained. Most of 
whole surface with green. At sea, though singly in- 
them are invisible to the naked eye, and species have 
visible, they produce one kind of the phosphorescent 
been described from l-1500th to l-2000th of a line 
light so often observed in the ocean. Formerly, before 
in length. So exceedingly minute, indeed, are they. 
their history was well understood, they were errone- 
that it is calculated a moderate-sized drop of water 
ously considered to derive their being, directly and 
may contain five hundred millions of these minims of 
spontaneously, from the decomposition of animal or 
creation ! They are of very simple organization, as 
vegetable matter in water, and were, from their sudden 
they are furnished with neither vessels nor nerves, are 
appearance in such situations, and in such immense 
not S3'mmetrical, have not distinct sexes, have no 
numbers, held to prove the truth of what is called 
visible eggs, and are without determined or permanent 
“ spontaneous generation.” Infusoria can resist a de- 
digestive cavity. The chief organs of which they 
gree of cold equal to 8° of Fahrenheit, and a degi'ee of 
are composed appear to be internal spherical cavities. 
heat equal to 260° Fahrenheit. According to Ehren- 
which frequently contain foreign particles supposed to 
berg, who has studied these creatures with great care, 
serve as food, and which are derived from the sur- 
they are divided' into two large groups, which he de- 
rounding water, entering into the substance of the body. 
nominates Polygastrica and Rotifera. 
and moving through it by the general contraction of 
This latter group, however, has now been proved to 
the mass, and being expelled through the opposite 
be of a much higher organization than the former, and 
side. Some have no visible locomotive organs, others 
has accordingly been removed from the class Infusoria 
have; and these are either cilia, or changeable processes. 
into a separate class by itself, allied to the Crustacea. 
as they are called— expansions of the substance of the 
The Polygastrica have also been proved to contain 
body. The substance itself which forms the body is 
whole families and sections which are not true Infusoria. 
called Sarcode, and in perhaps the greater number is 
Thus the Diatomacecc and Desmidiacece have been 
a glutinous, homogeneous, or slightly granular diapha- 
proved to be forms of Algm. The Vibrionina are now 
nous mass. In some Infusoria red specks are visible, 
which resemble ej'es, and by some zoologists are really 
included amongst the Oscillator ecc, a family of com- 
pound Algce; whilst the Volvocina and Monadina are 
considered as such ; though, from a want of all traces 
ascertained to be other forms of that large order of 
of a nervous system, and possessing no distinguishable 
plants. On the other hand, many others are appa- 
cornea or lens, others deny them to be true eyes, and 
rently only the larva state of Annelides. The genus 
compare them to the red specks often seen in Algae. 
Paramecium^ for example, has been ascertained to be 
The food of the Infusoria consists partly of vegetables. 
the embryo state of Planaria, and the genus Cercaria 
and partly of animal decomposing matter, and they 
to be the undeveloped young of an intestinal worm ; 
not unfrequently prey upon each other. They are the 
and lastly, two whole families containing the genera 
prey, again, of other aquatic animals; and as they 
Amiba, Arcellina, &c., have been removed to form part 
occur in immense quantities in the water of the ocean. 
of the following order, Rhizopoda. 
as well as in that of our fresh-water pools and slow 
The greater portion of the fossil Infusoria described 
running streams, they contribute much to the nourish- 
by naturalists as so abundant in the marine and fresh- 
ment of animals of a higher ordet which are useful to 
water deposits, are in like manner removed from this 
man. This has been particularly observed in the ocean. 
class and placed amongst the Diatomacecc. Tliough 
