Jerry,

 I make reference to Henderson in my descriptive guide to Mark
Twain, entries 66 and 266. I have Duckworth and Company as publishers
for the 1911 publication of _Mark Twain_.  The second entry is actually
for Arthur Scott's _Mark Twain: Selected Criticism_.  Scott here
includes a psychologically probing essay on Twain.

Jason G. Horn, Ph.D
Gordon College
Barnesville, GA 30204