X PREFACE. 



wlierever it seemed to me that the passages would 

 })e suihciently intelligible to a general reader. 

 I may observe, however, that although I ha\-o 

 throughout kept in view the requirements of a 

 general reader, I have also sought to render the 

 book of service to the working physiologist, by 

 brinsfinix tooether in one consecuti\ e account all the 

 more important observations and results which 

 liave been yielded by this research. 



G. J. R. 



IX)NDON, 1884. 



