IX THE HISTORY AND SCOPE OF ZOOLOGY 365 



The knowledge of the anatomical facts of cellular 

 development and cellular structure necessarily gave 

 immensely increased precision to the notion of grada- 

 tion of structure in the animal series from simple to 

 complex, and rendered Darwin's doctrine the more 

 readily accepted. It was not, however, until after 

 Darwin's date (1859) that the existence of unicellular 

 animals was fully admitted, and the general facts of 

 cellular Embryology established throughout the animal 

 kingdom. 



Similarly cellular Physiology, by establishing the 

 conception of a simple optically homogeneous cell- 

 substance as the seat of the activities which we call 

 " life/' rendered it possible to accept the suggestion 

 of a simple " substance of life " which might have 

 been evolved from simpler non-living matter by 

 natural processes depending on physical and chemical 

 laws. It is noteworthy that Darwin himself appears 

 not to have been influenced directly by any such 

 physiological or chemico-physical doctrine as to "proto- 

 plasm " or cell-substance. Nevertheless the way was 

 prepared for the reception of Darwin's theory by this 

 state of physiological knowledge. 



The word " protoplasm" requires a little further 

 notice. Protoplasm was applied by Von Mohl and 

 by Max Schultze to the slimy substance of the cell, 

 including therein both the general thinner material 

 and the nucleus. It is, as Eoscoe remarked at 

 Manchester (Brit. Ass. Address, 1887), a structure 

 and not a chemical body. Nevertheless gradually 

 physiologists have come to use the word " protoplasm " 



