HEREDITY. 



CHAPTER I. 



WHAT IS HEREDITY? 



The development of an animal, with the complex and beautiful 

 structural adjustments, the instincts, habits, and individual 

 traits of its parents is one of the most wonderful phenomena 

 of the material universe — Heredity is not due to the external 

 conditions which act upon the ovum, but to somethiui^ within 

 the ovum itself — The phenomena of reversion — Asexual and 

 sexual hereditj^ — Possibility of an explanation of heredity — 

 Characteristics which are now hereditary were at one time new 

 variations — Heredity and variation are opposite aspects of the 

 same problem — We may hope tiiat a more perfect acquaintance 

 with the laws of heredity will remove many objections to the 

 theory of natural selection. 



To the ordinary unscientific reader the word heredity 

 may perhaps suggest nothing more than a few curious 

 cases where an odd peculiarity of the parent has been 

 transmitted to the children, or it may recall the heredi- 

 tary transmission of a tendency to certain diseases, or the 

 mental or moral idiosyncrasies of the parents. 



To the breeder of domestic animals or plants it has a 

 somewhat wider significance, and recalls the transmission 

 by choice or fancy breeds of the features which give them 

 their value. To him heredity is the law wdiich enables 

 him to modify his animals and to build up and perpetu- 

 ate new varieties. 



