36 AN INTRODUCTION TO ZOOLOGY 



that Kolliker, Remak, Nageli, and Hofmeister opened the way 

 to an understanding of the nature of embryological develop- 

 ment, and the law of genetic continuity lying at the basis of 

 inheritance. It was the cell-theory again which, in the hands 

 of Goodsir, Virchow, and Max Schultze, inaugurated a new era 

 in the history of physiology and pathology, by showing that all 

 the various functions of the body, in health and in disease, are 

 but the outward expressions of cell activities. And at a still 

 later day it was through the cell-theory that Hertwig, Fol, Van 

 Beneden, and Strasburger solved the long-standing riddle of the 

 fertilization of the egg and the mechanism of hereditary trans- 

 mission. No other biological generalization, save only the theory 

 of organic evolution, has brought so many apparently diverse 

 phenomena under a common point of view, or has accomplished 

 more for the unification of knowledge. The cell-theory must 

 therefore be placed beside the evolution-theory as one of the 

 foundation stones of modern biology " (25, p. i). 



