DEVELOPMENT OF ZOOLOGY 523 



somes, the mitochondria as organized parts of the cell ; we have 

 learned of the texture and chemical qualities of protoplasm; 

 we have discovered the complexities of nuclear division and 

 the relation of cell structure and the behavior of the nuclear 

 units to heredity. It is impossible in a brief statement such as 

 this to discuss the whole list of brilliant investigators who have 

 had a part in this. The German biologists have been peculiarly 

 prolific in this work. The names of Nageli, von Mohl, Cohn; 

 De Bary, Virchow, and many others should be mentioned. 

 Boveri in 1900 first stated the law of the constancy of number 

 of chromosomes in the cells of any one species. Our own Ed- 

 mund B. Wilson of Columbia University has done as much as 

 any zoologist to delimit what has been accomplished from what is 

 yet to be done, and to stimulate the continual pushing forward 

 of the boundaries of our knowledge of intimate cell structure and 

 behavior. The last thirty years have been rich in American 

 contribution in this department of Zoology. 



518. Physiology. — Wm. Harvey (1578-1667), an English- 

 man, may be credited with the founding of physiology as an ex- 

 perimental science. His best known work was his demonstration 

 of the circulation of the blood. Haller (1708-17 7 7) studied 

 physiology as independent of human anatomy and medicine, 

 as a worthy science of its own. Johannes MuUer (1801-1858) 

 made a modern science of it. He brought to bear in its study the 

 comparative method which was so fruitful in anatomy, and. made 

 use of the microscope and of physics and chemistry in its inter- 

 pretation. His work has justly dominated the science until the 

 present. Following Muller and continuing his work were Du 

 Bois-Reymond (1818-1896), Claude Bernard (1813-1878), and 

 Liebig, a master in physiological chemistry. Michael Foster 

 of England and Verworn in Germany have done great work in 

 the subject in recent times. 



519. Embryology. — The beginnings of human thinking con- 

 cerning the origin and development of animals was even more 

 crude than in other realms of Zoology. Even Aristotle thought 

 that frogs and many other animals arose spontaneously from 

 mud, maggots from meat,' and the like. Redi (1626-1697), an 



