12 INTRODUCTION. 
sea, the cemetery of countless animalcules 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. To 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. 
Of all the sciences, Zoology 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 far-reaching 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 Zoology, 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 Physi- 
ology, Which is the study of the apparatus in action. The 
former is separated into Limbryology, or an account of the 
successive modifications through which an animal passes in 
its development from the egg to the adult state; and Wor- 
phology, 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 tis- 
sues, 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 or- 
gans 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 ani- 
mal 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 Zoology. 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; 
