THE 



POPULAR SCIENCE 



MONTHLY, 



AUGUST, 1914 



THE CELLULAE BASIS OF HEEEDITY AND 

 DEVELOPMENT 1 



Br Professok EDWIN GRANT CONKLIN 



PRINCETON UNIVERSITY 



A. Introductory 



HEREDITY is to-day the central problem of biology. This prob- 

 lem may be approached from many sides — that of the observer, 

 the statistician, the practical breeder, the experimenter, the embryolo- 

 gist, the cytologist — but these different aspects of the subject may be 

 reduced to three general methods of study, (1) the observational and 

 statistical, (2) the experimental, (3) the cytological and embryological. 

 Before taking up these different aspects of heredity it is important that 

 we should have clear definitions of the terms employed and a fairly 

 accurate conception of the processes involved. 



1. Definitions 



Heredity originally meant heirship, or the transmission of property 

 from parents to children, and in the field of biology it has been defined 

 erroneously as "the transmission of qualities or characteristics, mental 

 or physical, from parents to offspring" (Century Dictionary). The 

 colloquial meaning of the word has led to much confusion in biology, 

 for it carries with it the idea of the transmission from one generation 

 to the next of ownership in property. A son may inherit a house from 

 his father and a farm from his mother, the house and farm remaining 

 the same though the ownership has passed from parents to son. And 

 when it is said that a son inherits his stature from his father and his 

 complexion from his mother, the stature and complexion are usually 

 thought of only in their developed condition, while the great fact of 

 development is temporarily forgotten. Of course there are no "qual- 

 ities " or " characteristics " which are " transmitted " as such from one 

 generation to the next. Such terms are not without fault when used 



i Second of the Norman W. Harris Lectures for 1914 at Northwestern Uni- 

 versity on "Heredity and Environment in the Development of Men," to be pub- 

 lished by the Princeton University Press. 



vol. lxxxv. — 8. 



