[mcmurrich] presidential ADDRESS 3 



anus and Lamarck as early as 1802, but made familiar by Huxley 

 only in 1875. 



The doctrine of evolution, then, swept away specialism by estab- 

 lishing connections that linked up all lines of biological study. But 

 the stimulus it supplied to such studies led quickly to such a develop- 

 ment of them as to introduce another specialism, dependent upon the 

 extent of territory included and the diversity of the methods employed 

 in its cultivation. As a first result of the acceptance of the doctrine 

 there was an almost feverish haste on the part of zoologists to determine 

 as far as possible the genealogical affinities of the various animal groups, 

 ' and phylogenetic studies and speculations became a vogue. For 

 these embryological investigation held out the greatest promise and 

 to that line of study the productive energy of the great majority of 

 professional zoologists was directed for many years and with important 

 results. But as the studies progressed, attention gradually turned 

 from phylogenetic to ontogenetic problems, from studies of organo- 

 genesis and general larval development to questions as to the mode of 

 differentiation of the tissues of the individual, the cell-lineage of every 

 tissue of the developing organism being traced back to its origin in the 

 fertilized ovum. In such cell-lineage studies investigators were at 

 once brought face to face with the great problem of cell-differentiation 

 and inheritance; why in the developing embryo does one definite 

 cell under normal conditions always give rise to such and such a tissue, 

 while its sister cell gives rise to another quite different, and how, 

 amidst all this differentiation, is the inheritance of ancestral characters 

 maintained ? In brief, the confronting problems were those of the 

 mechanism of inheritance and the mechanism of differentiation, two 

 problems apparently and yet at the bottom but one and the same, the 

 obverse and reverse of the same coin. 



In the pursuit of the solution of these problems new methods 

 were developed and new fields of study were opened out. On the one 

 hand it was asked if differentiation takes place definitely thus and so 

 under normal conditions, what will happen if the conditions are made 

 abnormal ? No sooner was the question asked than it began to be 

 tested and the study of experimental morphology was revived, after 

 having remained in a state of suspended animation ever since the days 

 of Reaumur and Trembley. The methods employed were at first 

 rather crude and mechanical, but nevertheless they yielded important 

 results, such as clearer ideas as to the interdependence of the parts 

 in the developing embryo and a better understanding of the morpho- 

 logical conditions determining twin and monstrous births. 



Later changes in the chemical constitution of the environment 

 were employed to establish abnormal conditions and this method, by 



