PREFA7 ORY NOTE 



The substance of the greater part of this paper, which has 

 been in the present form for some time, was delivered, as a 

 lecture, at a Conversazione of the Royal College of Physicians 

 of Edinburgh, in the Hall of the College, on the evening of 

 Friday, the 3Oth of April last. 



It will be found to support itself, so far as the facts are 

 concerned, on the most recent German physiological literature, 

 as represented by Rindfleisch, Kiihne, and especially Strieker, 

 with which last, for the production of his " Handbuch," there 

 is associated every great histological name in Germany. 



EDINBURGH, October, 1869. 



