4 GENERAL ZOOLOGY 



while function, since it is concerned fundamentally with the pro- 

 duction of motion, is considered dynamic in nature. Such 

 distinction is of value in a general way only, since matter, and 

 particularly living matter, is constantly changing and therefore 

 never absolutely static. In other words, living objects like non- 

 living objects exist not only in a space relationship but also in a 

 pattern of time. The organism therefore should not be regarded 

 as matter (structure) plus motion (function) but rather as 

 matter in motion, or as structure in function. It is not necessary 

 to decide whether structure causes function or function causes 

 structure, for neither exists without the other. Structure and 

 function are complementary. 



Though structure and function considered separately have no 

 real meaning, for purely practical reasons the study of organisms 

 is pursued along two general lines, morphological and physio- 

 logical. Ideally, these should be carried out simultaneously or 

 as nearly so as possible, but for the beginning student it seems 

 best to begin by acquiring a sound knowledge of morphology as a 

 background for physiology. In such preliminary morphological 

 studies, questions as to the possible or probable functional 

 significance of structural relationships constantly arise. Such 

 questions should be raised even though a satisfactory answer may 

 not be forthcoming until a later time. Morphological detail is 

 meaningless without functional interpretation, nevertheless in 

 most cases a preliminary mastery of morphology facilitates the 

 attack on physiology and is the method followed in this book. 



Morphology and physiology are merely convenient terms for 

 classifying two fairly distinct groups of findings and the assign- 

 ment of a field of study under one head or the other is always 

 subject to some limitation. Thus embryology is ordinarily con- 

 sidered a morphological subject because its study consists to a 

 great extent in the examination and study in considerable detail 

 of the form and structure of embryos at different stages of devel- 

 opment ; but since this is done for the purpose of piecing together 

 a history of the process of development, an embryological study 

 that does not give due weight to the physiological aspects of 

 development becomes a series of lifeless descriptions of embryo 

 anatomy. 



By means of gross microscopic dissections of an animal, com- 

 bined with carefully planned laboratory experiments to demon- 



