NOTE. 
Volume 18 of the Contributions consists of 7 parts, which were 
issued as follows: 
Part 1, pages 1 to 68, June 17, 1914. 
Part 2, pages 69 to 86, April 16, 1914. 
Part 3, pages 87 to 142, February 11, 1916. 
Part 4, pages 143 to 172, March 3, 1916. 
Part 5, pages 173 to 224, October 30, 1916. 
Part 6, pages 225 to 260, September 22, 1917 (erroneously dated 
September 15, 1917). 
Part 7, pages 261 to 472, September 1, 1917 (erroneously dated 
August 18, 1917). 
Iv 
