INTRODUCTION

1. Definition of Zoology, and its Place among the Sciences. The province of Natural History is to describe, compare, and classify natural objects. These objects have been divided into the "organic" and the "inorganic," or those which are, and those which are not, the products of life. Biology is the science of the former, and Mineralogy the science of the latter. Biology again separates into Botany, or the Natural History of Plants, and Zoology, or the Natural History of Animals; while Mineralogy divides into Mineralogy proper, the science of mineral species, and Lithology, the science of mineral aggregates or rocks. Geology is that comprehensive knowledge of the earth's structure and development which rests on the whole doctrine of Natural History.

If we examine a piece of chalk, and determine its physical and chemical characters, its mode of occurrence and its uses, so as to distinguish it from all other forms of matter, we have its Mineralogy. But chalk occurs in vast natural beds; the examination of these masses their origin, structure, position, and relation to other rocks is the work of the Lithologist. Further, we observe that while chalk and marble are chemically alike, they widely differ in another respect. Grinding a piece of chalk so thin that we can see through it, and putting it under a microscope, we find imbedded in it innumerable bodies, about the hundredth of an inch in diameter, having a well-defined, symmetrical shape, and chambered like a nautilus. We cannot say these are

accidental aggregations, nor are they crystals; if the oyster shell is formed by an oyster, these also must be the products of life. Indeed, the dredge brings up similar microscopic skeletons from the bottom of the Atlantic. So we conclude that chalk is but the dried mud of an ancient sea, the cemetery of countless animals that lived and died long ago. The consideration of their fossil remains belongs to Paleontology, or that part of Biology which describes the relics of extinct forms of life. study the stratigraphical position of the chalk bed, and by the aid of its Paleontology to determine its age and part in the world's history, is the business of Geology.

To

Of all the sciences, Zoölogy is the most extensive. Its field is a world of varied forms — hundreds of thousands in number. To determine their origin and development, their structure, habits, distribution, and mutual relations is the work of the Zoologist. But so many and farreaching are the aspects under which the animal creation may be contemplated, that the general science is beyond the grasp of any single person. Special departments have, therefore, arisen; and Zoölogy, in its comprehensive sense, is the combined result of the labors of many workers, each in his own line of research.

Structural Zoology treats of the organization of animals. There are two main branches: Anatomy, which considers the constitution and construction of the animal frame; and Physiology, which is the study of the apparatus in action. The former is separated into Embryology, or an account of the successive modifications through which an animal passes in its development from the egg to the adult state; and Morphology, which includes. all inquiries concerning the form of mature animals, or the form and arrangement of their organs. The microscopical examination of any part, especially the tissues, belongs to Histology. Comparative Zoology is the com

parison of the anatomy and physiology of all animals, existing and extinct, to discover the fundamental likeness underneath the superficial differences, and to trace the adaptation of organs to the habits and spheres of life. It is this comparative science which has led to such grand generalizations as the unity of structure amidst the diversity of form in the animal creation, and by revealing the degrees of affinity between species has enabled us to classify them in natural groups, and thus laid the foundation of Systematic Zoölogy. When the study of structure is limited to a particular class or species of animals, or to a particular organ or part, monographic sciences are created, as Ornithotomy, or anatomy of birds; Osteology, or the science of bones; and Odontography, or the natural history of teeth.

Systematic Zoology is the classification or grouping of animals according to their structural and developmental relations. The systematic knowledge of the several classes, as Insects, Reptiles, and Birds, has given rise to subordinate sciences, like Entomology, Herpetology, or Ornithology.1

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Distributive Zoology is the knowledge of the successive appearance of animals in the order of time (Paleontology in part), and of the geographical and physical distribution of animals, living or extinct, over the surface of the earth.

Theoretical Zoology includes those provisional modes of grouping facts and interpreting them, which still stand waiting at the gate of science. They may be true, but we can not say that they are true. The evidence is incomplete. Such are the theories which attempt to explain the origin of life and the origin of species.

Suppose we wish to understand all about the horse. Our first object is to study its structure. The whole

*See Notes at the end of the volume,

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