PART II 



COMPARATIVE MORPHOLOGY 



Anatomy can be studied either by taking type forms of the dif- 

 ferent classes and completing one before beginning the next; or 

 by studying all of the types comparatively, one system of or- 

 gans at a time. The former is systematic anatomy and was the 

 method used in the first part of this text. The latter is systemic 

 anatomy, and presupposes some knowledge of the animals to 

 be studied. The following chapters on morphology, or form, con- 

 sider the organs and systems of organs in relation to their devel- 

 opment and completed structure. 



Each system is traced from the simpler to the more complex, 

 both from the standpoint of individual development (ontogeny) 

 and racial development (phylogeny). Sufficient information has 

 been given about natural history and embryology to show that 

 each organism is an individual, and that each group is more or 

 less definitely separated from others; but the student has un- 

 doubtedly realized that there are underlying relationships be- 

 tween groups, just as there is a relationship between the organs 

 of the body. Thus, from the standpoint of evolution, the classes 

 and orders of the vertebrates are but units in a coordinated 

 whole. 



The fundamental unity of development that is found in the 

 races of vertebrates is also true of the organs of the body. In 

 the preceding embryological discussions, and in the chapters 

 which follow, each system has been considered as a unit. But, 

 although this is convenient for study, independence of organs 

 is never true functionally for each system is dependent upon 

 every other; and the individual is not a group of discrete or- 

 ganic units, but a coordinated whole. 



The stress which is generally placed upon laboratory dissec- 

 tions applies particularly to the study of comparative mor- 

 phology. The anatomical facts should be gained at first hand 

 from a study of the animals themselves, and the best that a 

 book can do is to correlate these more or less isolated details into 

 a coherent scheme. A text, however, cannot replace the knowl- 

 edge gained in the laboratory. 



