12 
INTRODUCTION. 
less animals that lived and died long ago. The considera¬ 
tion 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 contem¬ 
plated, 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 re¬ 
sult 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 or¬ 
gans. The microscopical examination of any part, especial¬ 
ly the tissues, belongs to Histology. Comparative Zoology 
is the comparison of the anatomy and physiology of all ani¬ 
mals, existing and extinct, to discover the fundamental like¬ 
ness 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 gen¬ 
eralizations 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 
Zoology. When the study of structure is limited to a par¬ 
ticular class or species of animals, or to a particular organ 
or part, monographic sciences are created, as Ornithotomy , 
