BRIEF HISTORY OF THE SCIENCE OF ZOOLOGY 469 



Balfour and their numerous pupils. In Germany, Russia, 

 and France the workers were even more abundant, and 

 America includes as its share the work of Agassiz and of men 

 still active. 



Cytology. — Wlien thin sections of plant tissues were first 

 looked at with a microscope, they were seen to be made up of 

 spaces surrounded by thick walls, and these were called " cells." 

 Similar cells were seen in animal tissues also. But it was not 

 until 1838-1839 that the botanist Schleiden and the zoologist 

 Schwann raised these isolated facts to a theory by declaring 

 that the whole body of organisms is made up of such cells and 

 their products. It was, however, left to Schultze to bring out 

 the more fundamental idea that the Ijody is made up of a living 

 substance — protoplasm — which is divided for physiological 

 purposes into more elementary parts called cells. Later it was 

 discovered that the activitj^ of each cell is controlled by a central 

 body, or nucleus, and for the last three or four decades the 

 behavior of the nucleus in cell division and in heredity has 

 been the object of extensive investigation. 



The Evolution Theory. — We have seen how the Greeks 

 regarded the evolution of the organic world as a part of cosmic 

 philosophy. Through a narrow interpretation of the Mosaic 

 account of creation, the Christian church was led away from 

 those broad views, and in this attitude it was supported by Lin- 

 nseus and others. We have seen that a French school of evolu- 

 tion arose, but its explanation of the method of evolution was 

 not acceptable, and the school was crushed by the authority of 

 Cuvier. In England there were not wanting those who accepted 

 or promulgated the theory with, a very slight basis of fact. 

 It was the great service of Charles Darwin to offer such a 

 theory, accompanied by proofs so niunerous and presented in a 



