HEREDITY. 423 



gional influences and to a combination of causes ; and 

 of those of acquired plasticity and adaptation. I com- 

 mence with an example of the 



a. Inheritance of Characters Due to Nutrition. 



"One class of ' acquired characters/ the transmis- 

 sion of which by heredity is especially denied by Weis- 

 mann, includes all 'those which are directly due to 

 nutrition.' 



"This denial strikes at the very foundation of what 

 has heretofore been considered an essential factor in 

 the practical improvement of breeds as to size. The 

 size attained by adult, healthy domestic animals de- 

 pends practically upon two causes heredity and nu- 

 trition. Heredity is of course the chief one, for no 

 amount of feeding will make the Shetland pony equal 

 the Norman horse in size ; but whatever the heredity, 

 the size of the adult individual as compared with the 

 average of others of the same breed depends usually 

 upon its food. The ultimate weight of the mature 

 animal varies of course with the amount of fat assimi- 

 lated, which may occur long after maturity ; but the 

 size as dependent upon the frame, such as the weight, 

 length, and* general proportions, is modified by the 

 quantity and quality of food available during the grow- 

 ing period of early life. This fact no one questions ; 

 and if these acquired characters are in no degree what- 

 ever transmitted, then certain practices of breeders, 

 which are founded upon the contrary belief are delu- 

 sive and expensive mistakes. 



"Practical breeders have hitherto believed that 

 these characters are to some degree transmitted, and 

 practice accordingly. I have searched extensively the 

 writings of practical breeders to see if I could find a 



