THE STUDY OF STRUCTURE. 359 



of the general problems of biology, notably in regard 

 to heredity and inheritance. 



The student who wishes to understand the position 

 of cellular biology at the beginning of the twentieth 

 century should read a luminous book by Prof. E. 

 B. Wilson (The Cell in Development and Inherit- 

 ance, 2nd ed., 1900), along with which we may cite 

 Delage's La structure du protoplasma et les theories 

 sur I'heredite et les grands problemes de la biologic 

 generate (1895). From Wilson's work, we venture 

 to quote the first paragraph : 



"During the half-century that has elapsed since the 

 enunciation of the cell-theory by Schleiden and 

 Schwann, in 1838-39, it has become ever more clearly 

 apparent that the key to all ultimate biological prob- 

 lems must, in the last analysis, be sought in the cell. 

 It was the cell-theory that first brought the structure 

 of plants and animals under one point of view, by re- 

 vealing their common plan of organisation. It was 

 through the cell-theory that Kolliker, Kemak, Nageli, 

 and Hofmeister opened the way to an understanding of 

 the nature of embryological development, 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 expression 

 of cell-activities. And at a still later day it was 

 through the cell-theory that Hertwig, Fol, Van Bene- 

 den, and Strasburger solved the long-standing riddle 

 of the fertilisation of the egg and the mechanism of 

 hereditary transmission. No other biological general- 

 isation, 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 there- 



