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, 



