An Outline of the History of Biology. 9 



The demonstration of the marvellously exact bipartition 

 of nuclear elements; the discovery of the centrosomes, 

 which appear to act as dynamic centres in cell-division ; 

 the experimental proof that a cell bereft of its nucleus 

 may move and feel for a time, but cannot assimilate or 

 secrete; and the growth of criticism as to the adequacy 

 of the cell-theory, may be noted as representative steps 

 in modern cytology. 



In regard to development, the most momentous step 

 has been the recognition of germinal continuity. The 

 unique potentiality of the germ-cells depends upon 

 their continuity through successive cell-generations with 

 the germ-cells of the parent organism. We may 

 associate this doctrine with the name of Weismann. 



Also of great importance is the renewed attack on the 

 problems of physiological embryology, and the discovery 

 of some ingenious experimental methods, in connec- 

 tion with which the names of Roux and O. Hertwig are 

 especially prominent. And although no answer is yet 

 forthcoming, there has been a clearer statement than 

 heretofore of the fundamental question : Is the path of 

 embryonic development definitely predetermined in the 

 organization of the germ-cells; or is the path, so to 

 speak, mapped out, as development goes on, by the 

 varied relations and conditions to which the embryonic 

 cells are exposed? 



Palaeontology has risen to high dignity as a branch 

 of biology, its results being now universally recognized 

 as the surest contributions to the history of life upon 

 the earth. The distinction between the anatomist and 

 the "fossilist" has disappeared, both being now equally 

 morphological and evolutionary. We may connect the 

 change with the name of Zittel. 



Among the characteristics of modern physiology we 

 may notice the slow but important development of com- 

 parative work, with its evidence that there is unity amid 

 diversity in vital processes; the increased concentration 

 on the problems of metabolism (the chemical changes of 

 the living body); the application of physiological results 

 and methods to the problems of development; and the 

 rise of a school of " neo-vitalists ", who have helped to 



