12 INTRODUCTION 



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 simi- 

 lar 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. 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 comprehen- 

 sive 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 con- 

 siders the constitution and construction of the animal 

 frame ; and Physiology, which is the study of the appara- 

 tus 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 micro- 

 scopical examination of any part, especially the tissues, 

 belongs to Histology. Comparative Zoology is the com- 



