1 6 GENERAL PRINCIPLES OF ZOOLOGY. 



difference between the shabby drawings of an Aldrovandus 

 and the quite masterly figures of a Lyonet or a Rosel von 

 Rosenhof. 



Period of Comparative Anatomy. Thus through the 

 zeal of numerous men filled with a love of nature a rich ana- 

 tomical material was collected, which needed only a mental 

 reworking; and this mental reworking was brought about, 

 or at least entered upon, by the great comparative anato- 

 mists, who lived at the end of the previous, and the begin- 

 ning of the present century. Among these are especially 

 to be named the French zoologists Lamarck, Savigny, 

 Geoffroy St. Hilaire, Cuvier, and the Germans Meckel and 

 Goethe. 



Correlation of Parts. When the separate animals 

 were compared with one another with reference to their 

 structure there was obtained a series of important funda- 

 mental laws, particularly the law of the Correlation of Parts 

 and the law of the Homology of Organs. The former 

 established the fact that there exists a dependent relation 

 between the organs of the same animal, that local changes in 

 one single organ also lead to corresponding changes at some 

 distant part of the body, and that therefore from the con- 

 stitution of certain parts an inference can be drawn as to 

 the constitution of another part of the body. Cuvier par- 

 ticularly made use of this principle in reconstructing the 

 aspect of extinct animals. 



Homology and Analogy. Still more important was 

 the theory of the Homology of Organs. In the organs of 

 animals they learned to discriminate between an anatom- 

 ical and a physiological character; the anatomical character 

 is the sum of all the anatomical characteristics, as found in 

 form, structure, position, and mode of connection of 

 organs; the physiological character is their function. 

 Anatomically similar organs in closely related animals will 

 usually have the same functions, as, for example, the liver 

 of all vertebrates has the function of preparing gall ; here 

 anatomical and physiological characteristics go hand in 

 hand. But this need not necessarily be the case; very 



