INTRODUCTION. 13 



would be as crude as if we attempted to form conclusions 

 as to his zoological position without reference to other 

 species of animals. 



In the ensuing chapters the following plan has been 

 adopted : The effects of increased use and disuse of 

 parts is considered in connection with the gradual change 

 in the function of organs, and the part played by the 

 transmission of the effects of increased use and disuse in 

 producing vestigial structures in complex organisms. 

 The tendency of vestiges to become diseased or to give 

 rise to conditions disadvantageous to the individual is 

 fully dealt with. The important and interesting subject of 

 the transmission of acquired characters and malforma- 

 tions is briefly discussed, and a chapter is devoted to 

 causes of disease arising without the organism and the 

 relation they bear to the remarkable processes, inflamma- 

 tion and fever. Tumours are considered in connection 

 with general morbid processes, and the scanty knowledge 

 we possess of the zoological distribution of disease is 

 summarized. 



