2 AN INTRODUCTION TO ZOOLOGY 



group being considerable, not obliterated by intermediate forms, 

 and inherited from generation to generation." Another promi- 

 nent zoologist, when asked for a definition of a species, said it 

 was " somebody's opinion." He did not mean that species are 

 not realities in nature, but that just how many are represented 

 in a particular group must usually be determined by competent 

 authority. 



Distributional Zoology attempts to ascertain the past and 

 present habitats of animals, as well as the factors which control 

 their distribution over the surface of the earth. The study of the 

 distribution of recent animals is known as Zoogeography, and that 

 of fossil forms constitutes a part of the science of Paleontology. 



Animal Morphology is the science of form and structure. That 

 part of it which pertains to the gross dissection of organs is known 

 as Anatomy; that which relates to the microscopic study of 

 tissues, as Histology. If, however, a study is concerned with the 

 development of animals, organs, or tissues, it is included in the 

 science of Embryology. 



Animal Physiology deals with the functions of the parts of 

 animals. 



Animal Ecology is the study of the relationships of animals 

 to one another and to their environment. 



Evolutionary Zoology is concerned with the origin and descent 

 of the different species of animals. 



Paleozoology is the study of fossil remains of animals. It is 

 intimately associated with all the other branches of zoological 

 science, except the study of physiological processes. The physi- 

 ology of extinct forms can only be inferred from the study of 

 the activities of recent animals. Owing to the fact that fossils 

 are usually embedded in stone, the mechanical appliances which 

 are used in studying them are necessarily quite different from 

 those employed in the investigation of modern animals. 



The different branches of zoological science are closely related 

 and mutually interdependent; for example, the students of evo- 

 lution gain evidence concerning the ancestry of animals from 



