ON THE EFFECT OF CONTINUED ADMINISTRATION 



OF CERTAIN POISONS TO THE DOMESTIC FOWL, 



WITH SPECIAL REFERENCE TO THE 



PROGENY.! 



By RAYMOND PEARL. 



I. The Problem. 



(Read April 75, 7916.) 



One of the outstanding problems of genetics is that of the origin 

 of new heritable variations. W^ith the passage of time and the 

 accumulation of exact experimental data it becomes increasingly 

 clear that this factor is the basic one in all evolutionary change, 

 whether progressive or retrogressive. Just now it is the fashion to 

 speak of new heritable variations as mutations, but such designation 

 does not appear either to make the facts concerned any different 

 from what they were under an older terminology, nor does it 

 essentially contribute to our knowledge about them. Indeed it is, 

 so far as I can see, entirely fair to say that but little in the way of 

 essential advance has been towards the solution of this problem 

 since Darwin's examination and analysis of it. The two leading 

 students of variation since Darwin, Bateson and De Vries, have to 

 be sure, contributed greatly to our knowledge of certain aspects of 

 the phenomena of variation ; notably, on the one hand, in the direc- 

 tion of establishing a number of definite principles or laws of 

 morphogenesis which control or determine in large degree the 

 somatic expression of germinal differences, and, on the other hand, 

 in very precisely and minutely analyzing the genetic behavior of 

 various heritable variations, after they have appeared. But it is the 

 problem of the origin, the determination, the causes of those germinal 

 differences which lie behind somatic variations, and indeed are the 



1 Abstract of Paper No. 97 from the Biological Laboratory of the Maine 

 Agricultural Experiment Station. 



243 



