EVIDENCES OF EVOLUTION. 89 



At first classification was based on only superfi- 

 cial characteristics. Now we must take into account, 

 not only external form and internal structure, not 

 only anatomical and histological characteristics, but 

 we must also incorporate in our classifications the 

 teachings of embryology and cytology. We must 

 study not only bone and muscle, but investigate the 

 nature and structure of the cell, and study the 

 embryo from its earliest to its latest state of devel- 

 opment. We can now call no one master, for the 

 days of magister dixit have passed. Neither Aris- 

 totle, nor Linnaeus, nor Cuvier nor any other one 

 person is to be our sole guide, but we must per- 

 force elaborate a system from the combined ob- 

 servations and generalizations of not only the 

 great masters above-mentioned, but also from those 

 of Schwann and Von Baer, Johann and Fritz 

 Mu'ller, Kowalewsky and Darwin. We must dis- 

 card much, once accepted as true, which more ex- 

 act research has disproved, and combine into one 

 systematic whole the gleanings of truth which 

 are afforded by the investigations of so many stu- 

 dents in the various departments of natural knowl- 

 edge. 



Taxonomic Divisions. 



Our brief reference to some of the chief systems 

 of classification conducts us naturally to a more im- 

 portant topic, the nature of the various categories 

 which we have been considering. 



Have branches, classes, orders, families, genera 

 and species a real existence in nature, or are they 



