The volumes therefore necessarily contain many letters of a highly technical character, but none, we hope, which are not essentially interesting.

With a view to saving space, we have confined ourselves to elucidating the letters by full annotations, and have for the same reason--though with some regret--omitted in most cases the beginnings and endings of the letters.
For the main facts of Mr.Darwin's life, we refer our readers to the abstract of his private Diary, given in the present volume.
Mr.Darwin generally wrote his letters when he was tired or hurried, and this often led to the omission of words.

We have usually inserted the articles, and this without any indication of their absence in the originals.

Where there seemed any possibility of producing an alteration of meaning (and in many cases where there is no such possibility) we have placed the introduced words in square brackets.

We may say once for all that throughout the book square brackets indicate words not found in the originals.