CHAPTER III- 



THE CELLULAR BASIS OF HEREDITY AND 

 DEVELOPMENT 



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 embry- 

 ologist, the cytologist; but these different aspects of the subject 

 may be reduced to three general methods of study, (i) the ob- 

 servational and statistical, (2) the experimental, (3) the cyto- 

 logical and embryological. We have dealt with the first and sec- 

 ond of these in the preceding chapter and before taking up the 

 third it is important that we should have clear definitions of the 

 terms employed and a fairly accurate conception of the processes 

 involved. 



1. Confused Ideas of Heredity. — Heredity originally meant the 

 transmission of property from parents to children, and in the 

 field of biology it has been defined erroneously as "the transmis- 

 sion of qualities or characteristics, mental or physical, from par- 

 ents to offspring." 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 



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