Of letters addressed to my father I have not made much use. It was his
custom to file all letters received, and when his slender stock of files
("spits" as he called them) was exhausted, he would burn the letters of
several years, in order that he might make use of the liberated "spits."
This process, carried on for years, destroyed nearly all letters received
before 1862. After that date he was persuaded to keep the more interesting
letters, and these are preserved in an accessible form.

I have attempted to give, in Chapter III., some account of his manner of
working. During the last eight years of his life I acted as his assistant,
and thus had an opportunity of knowing something of his habits and methods.

I have received much help from my friends in the course of my work. To
some I am indebted for reminiscences of my father, to others for
information, criticisms, and advice. To all these kind coadjutors I gladly
acknowledge my indebtedness. The names of some occur in connection with
their contributions, but I do not name those to whom I am indebted for
criticisms or corrections, because I should wish to bear alone the load of
my short-comings, rather than to let any of it fall on those who have done
their best to lighten it.

It will be seen how largely I am indebted to Sir Joseph Hooker for the
means of illustrating my father's life. The readers of these pages will, I
think, be grateful to Sir Joseph for the care with which he has preserved
his valuable collection of letters, and I should wish to add my
acknowledgment of the generosity with which he has placed it at my
disposal, and for the kindly encouragement given throughout my work.

To Mr. Huxley I owe a debt of thanks, not only for much kind help, but for