EASY LESSONS IN ANIMAL BIOLOGY.
CHAPTER I.
Biology is the science of life, the true doctrine concerning all living things. Animal biology is that branch of the science which relates to animals, as distinguished from plants. It tells of these animals what we know about them, where and how they live, what food they eat, how it is received, and how they grow and multiply. Of all the sciences, this seems most extensive, having for its field a world of numberless forms, alike in that they all live, and have some characteristics in common, yet showing great diversity in their structure, appearance, and mode of life. In this summary of facts we shall simply classify, or methodically arrange in groups, according to their distinguishing peculiarities, the members of this vast family.
The animal kingdom is divided into the following sub-kingdoms, each of which is subdivided into classes. The following table shows these divisions in their proper order, beginning with the lowest:
| Sub-kingdom I—Protozoa. | { Class I—Monera. { Class II—Gregarinida. { Class III—Rhizopoda. { Class IV—Infusoria. |
| Sub-kingdom II—Spongida. | |
| Sub-kingdom III—Cœlenterata. | { Class I—Hydrozoa. { Class II—Anthozoa. { Class III—Ctenophora. |
| Sub-kingdom IV—Echinodermata. | { Class I—Crinoidea. { Class II—Asteroidea. { Class III—Echinoidea. { Class IV—Holothuroidea. |
| Sub-kingdom V—Vermes. | { Class I—Flat Worms. { Class II—Round or Thread Worms. { Class III—Rotifera. { Class IV—Polyzoa. { Class V—Brachiopoda. { Class VI—Annelidæ. |
| Sub-kingdom VI—Mollusca. | { Class I—Lamellibranchiata. { Class II—Gasteropoda. { Class III—Cephalopoda. |
| Sub-kingdom VII—Articulata. | { Class I—Crustacea. { Class II—Arachnida. { Class III—Myriapoda. { Class IV—Insecta. |
| Sub-kingdom VIII—Tunicata. | |
| Sub-kingdom IX—Vertebrata. | { Class I—Pisces. { Class II—Reptilia. { Class III—Aves. { Class IV—Mammalia. |
SUB-KINGDOM I.
Protozoa (first animals). These earliest formed animals are distinguished for the simplicity of their structure. In some cases their animal nature was long ago in doubt, and they were, for a time, put down as probably belonging to the vegetable kingdom. The border line between the two has never been very definitely located. Biologists may fail to tell just what special quality distinguishes the minute animal from the microscopic plant. This is not wonderful, when it is remembered that myriads of animals, known to be such, are so small that it requires a lens of strong magnifying power to discover them. Three thousand of them, placed side by side, would make a line but little over an inch long.
Class I.—Monera (single). These are the simplest forms of microscopic aquatic animals. They are entirely homogeneous, and without any developed organs; mere particles, of a jelly-like, but living, or life-supporting substance, called protoplasm, or more properly, bioplasm. This, all admit, is the physical basis of life, and the medium of its manifestation, just as the conductor is a medium of manifestation of electricity. But is it not a stupid blunder to confound the mere medium of its manifestation with the life itself? In neither case is the recognized physical basis of the manifestation necessary to the existence of that manifested by its means. Electricity exists without the conductor, and life may exist without the bioplasm.