INTRODUCTION 



19 



There is always a considerable volume of evidence which supports the 

 theory and gives all indication that it is a true statement. Finally, 

 the theory advances to a principle or law after it has been so thor- 

 oughly and critically tried as to be generally accepted and assumed 

 as a truth. This process requires the accumulation of the combined 

 restilts of numerous investigators over a long period of time. To 

 many people truth is absolute, not relative, and a conclusion once 

 drawn is fixed and may not be withdrawn for any reason. In 

 science conclusions are always subject to modification or even 

 abandonment as investigation continues. Scientific hypotheses are 

 frequently shown to be untenable, theories are occasionally found 

 fallacious and discarded, but up to the present time our scientific 

 principles have remained valid. However, at any time sufficient 

 evidence is produced to show the absolute fallacy of a so-called 

 principle, the scientist will put aside sentiment and prejudice and 

 accept the results of repeated investigation. Science is, therefore, 

 a chajiging, increasing body of knowledge which is ever becoming 

 more thoroughly established. 



Zoology, a Biological Science 

 The name, zoology, which is derived from the Greek words zoos, 

 animal, and logos, discourse on, refers to the study or science of 

 animals. The natural sciences, as distinguished from the social 

 sciences, are conveniently divided into two groups: the physical 

 sciences, such as chemistry, physics, and astronomy, which deal with 

 nonliving bodies; and the biological sciences, such as botany and 

 zoology, which are concerned with living organisms. Zoology and 

 botany together constitute the science of biology. The expression 

 animal hiologij is often used as a synonym for zoology. A person 

 who specializes in the study of zoology is known as a zoologist. There 

 was at one time an erroneous popular impression that zoologists were 

 simply "bug-hunters." This conception of the field has been greatly 

 expanded until now it is considered one of the valuable and serious 

 fields of science. 



The Subdivisions of Zoology 



Although zoology is only one of the divisions of the general field 

 of biological science, it is such a broad field in itself that it is neces- 

 sary to subdivide it into several divisions for convenience in study. 

 It has been a relatively short time since all of the known biology, 

 geology, and related subjects were studied under the head of natu- 



