PEEFACE. 



THE changes in the present Edition of Part II. are neither 

 many nor great, being such only as seemed to be rendered 

 necessary by the progress of knowledge. I have received much 

 help from the friends who have helped me before, more parti- 

 cularly from my old friend Dr A. Sheridan Lea ; and my thanks 

 are also especially due to my younger friend, Dr H. K. Anderson, 

 who has much assisted me with the proofs. A separate index to 

 the Part has been added. 



CAMBRIDGE, 



March, 1895. 



