we must ask the reader's patience, and beg him to believe that some pains
have been devoted to arrangement.

Mr. Darwin, who was careful in other things, generally omitted the date in
familiar correspondence, and it is often only by treating a letter as a
detective studies a crime that we can make sure of its date. Fortunately,
however, Sir Joseph Hooker and others of Darwin's correspondents were
accustomed to add the date on which the letters were received. This
sometimes leads to an inaccuracy which needs a word of explanation. Thus a
letter which Mr. Darwin dated "Wednesday" might be headed by us "Wednesday
[January 3rd, 1867]," the latter half being the date on which the letter
was received; if it had been dated by the writer it would have been
"Wednesday, January 2nd, 1867."

In thanking those friends--especially Sir Joseph Hooker and Mr. Wallace--
who have looked through some of our proof-sheets, we wish to make it clear
that they are not in the smallest degree responsible for our errors or
omissions; the weight of our shortcomings rests on us alone.

We desire to express our gratitude to those who have so readily supplied us
with information, especially to Sir Joseph Hooker, Professor Judd,
Professor Newton, Dr. Sharp, Mr. Herbert Spencer, and Mr. Wallace. And we
have pleasure in mentioning Mr. H.W. Rutherford, of the University Library,
to whose conscientious work as a copyist we are much indebted.

Finally, it is a pleasure to express our obligation to those who have
helped us in the matter of illustrations. The portraits of Dr. Asa Gray,
Mr. Huxley, Sir Charles Lyell, Mr. Romanes, are from their respective
Biographies, and for permission to make use of them we have to thank Mrs.
Gray, Mr. L. Huxley, Mrs. Lyell, and Mrs. Romanes, as well as the