i8 HERBERT SPENCER AND 



theory or the other, we find that it is preponderantly 

 in favour of Weismann's. 



In the last two decades a large and active school of 

 Experimental Morphology and Embryology has come 

 into existence, whose object it is to inquire into the 

 very problems that we are considering. Started by 

 Oscar Hertwig, Roux, Hans Driesch, Boveri, and many 

 others on the Continent, this method of investigation 

 has been taken up with great enthusiasm in America 

 by E. B. Wilson, Morgan, Jacques Loeb, and many 

 others, but it has as yet made very little progress in this 

 country. In Oxford, however, it has distinguished 

 representatives in the persons of Dr. Vernon and Dr. J. W. 

 Jenkinson, and I hope that in the near future this 

 University will be the English centre of this form of 

 zoological research, which is the complement of that 

 branch of inquiry into the hereditary transmission of 

 structure and characters which has been so firmlv 

 established at Cambridge. The first step to be taken 

 by this school of developmental mechanics was a 

 renewed and much more detailed inquiry into the way 

 and course of the development of the germ-cell into the 

 embryo. 



The earlier embryologists were contented with saying 

 that the ovum divided into two, the two into four, the 

 four into eight, and so forth. That the cells formed 

 by repeated divisions arranged themselves into a hollow 

 sphere or blastula : that one half of this sphere became 

 tucked into the other half to form a two-layered gastrula, 

 and thus two primary cell layers were formed — an outer 

 and an inner — from which by further differentiation all 

 the organs of the adult were eventually established. 



The more modern embryologists go much further than 

 this and trace the exact fate of every cell formed during 

 the division of the ovum. The time and place of origin 

 of every cell is noted, and its subsequent history is 

 followed, until it is satisfactorily proved what part of 



