646 PROTOZOA. 
€la§s I. IMFU80IIIA. 
This Class of Animals is one of the revelations of the microscope which is calculated to fill 
the mind with profound astonishment at the fullness and infinitude of animal life. Though gener- 
ally so minute as to elude the unaided vision, they are still of various forms and sizes, and are 
arranged by naturalists under various subdivisions. Nearly every drop of water on the surface of 
the globe appears to contain them in greater or less profusion some of them are not more than one 
two-thousandth of an inch in length, and even the generality of the race do not exceed one-fiftieth 
of an inch. Eight hundred thousand millions may be contained in a cubic inch of water, and 
a thousand millions in a single drop of water ! Nevertheless, these creatures live, and have their 
being, and are marked with habits and capacities well worthy our consideration. They also 
seem to perform an immense work in the economy of nature. The progeny of some species 
amount to two hundred and sixty millions in a single month, thus supplying an incredible 
amount of food to the multitudinous generations of minute animals that inhabit the waters of 
the earth. We shall, however, be able to notice only a few of the more remarkable species, in- 
cluded in the orders which compose this class — Slomatoda and Astomata. 
ORDER 1. STOMATODA. 
This term is derived from the Greek, stoma, a mouth. The order includes several families, all 
of which are distinguished by the possession of a mouth. 
THE MONADID^. 
These consist of rounded or oval animalcules, each of which 
possesses a mouth, furnished with cilia, through which it is 
able to introduce into its substance, particles of solid matter 
which serve for its nutrition. One species is called the 
Twilight Monad, Monas crepusculum, from its being con- 
sidered as forming the unit of existence, the point from whence 
the glimmering spark of life first emerges out of the darkness 
of nonentity. It consists, says Gosse, " of a tiny speck of pel- 
lucid matter, rounded in form, and supposed from its move- 
ments and from analogy, to be furnished with a single cilium, 
by the lashing action of which it rows itself through the 
water. No words can convey an adequate idea of the size 
of an animal so minute as this ; but the imagination may be 
assisted by supposing a number of them to be arranged side 
by side in contact with each other, like the beads of a neck- 
lace, when twelve thousand of them would go comfortably 
within the length of a single inch. If we take a bunch 
of leaves of the common sage, for example, or a few twigs 
of hay, and, tying them into a bundle, suspend them in a jar 
of water, allowing the contents to remain untouched, but ex- 
posed to the air, some interesting results will follow. If 
we examine it on the second day, we shall find a sort of scum covering the surface and the 
* "It is a great error, which the common style of exaggeration in writing on such subjects has brought about, and 
which great numbers of people believe, that all water contains animalcules, and that every drop of water is filled 
with animal life. So far is this from the truth that, in ordinary clear water taken from the middle of a well or from 
the center of a spring, there is but little chance of finding animal life; and any creature discovered by the micro- 
scope in such water must be regarded as an estray from the mossy sides of the spring, or the chinks of the stones, and 
of the bucket in the well. But it is equally true that in the moss at the sides of the clearest spring, myriads of ani- 
malcules live, and a drop of water scraped with the green ooze from the old oaken bucket, overflows with animal 
VARIOUS FORMS OP ANIMALCULES MAGNIFIBD 
Fig. 1, Monads ; 2, Forms assumed by 
the Amcsba ; 3, Flask Animalcules, En- 
ehelis ; 4, AcUnoplirys sol; 5, Euglena 
viridis ; 6, Gonimm pectorale ; 7, Tr ache- 
lias anas; 8, Paramecmm aurelia ; 9, 
Navioula ; 10, Viby'io Spirillum ; 11, Vorti- 
cella Stentor. 
