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.