CHAPTER I 



Introduction 





Living as they did near the Mediterranean and Aegean seas 

 where tides receded and left animals upon the shore, and where 

 insects developed in decayed flesh, it was natural that the early 

 Greeks and Romans should believe in the spontaneous generation of 

 life. This belief persisted until the experiments of an Italian 

 naturalist, Redi, performed in 1688, showed that maggots originated 

 in meat from eggs laid by flies. In the middle of the nineteenth 

 century, Pasteur proved conclusively that not only larger organ- 

 isms, but even minute bacteria would not develop in sterilized media 

 unless they were introduced. 



We believe that all life came from pre-existing life — omne vivum 

 ex vivo — but it is not our purpose to discuss in this text the various 

 theories of how life came into being. • We are interested in the 

 science of all living things, Biology (Gr. bios, life; logos, discourse), 

 once termed Natural History, which includes the study of the struc- 

 ture and activities of both plants and animals. While we must 

 consider the plants in their relationship to animals, we cannot 

 include the study of Botany, but must confine ourselves to the 

 study of animals, called Zoology. 



The Function of Zoology.— The science of Zoology (Gr. zoon, 

 animal; logos, discourse) indicates to us the relationship of animals 

 from the unicellular to the most highly developed multicellular 

 organism, man. In order to understand an animal thoroughly, we 

 must know its anatomy, physiology, reaction to environmental 

 conditions, and its economic importance. 



Medicine in all its aspects owes a great debt to Zoology, not only 

 because of the opportunity to observe lower forms under favorable 

 circumstances, but also because of the important relationship of 

 parasitic animals to each other and to man. Some of the most 

 important discoveries in sanitation and preventive medicme, as 

 well as in surgery, have been made as a direct result of zoological 



studies. 



Agriculture owes much of its advancement to experimental work 



