PREFACE.
Yll
the broad facts of the case are of fundamental im¬ portance; and, so far as these are concerned, I ven¬ ture to hope that no error has slipped into my statement of them.
As for the details, it must be
remembered, not only that some omission or mis¬ take is almost unavoidable, but that new lights come with new methods of investigation; and that better modes of statement follow upon the improve¬ ment of our general views introduced by the gradual widening of our knowledge. I sincerely hope that such amplifications and rectifications may speedily abound; and that this sketch may be the means of directing the attention of observers in all parts of the world to the crayfishes. Combined efforts will soon furnish the answers to many questions which a single worker can merely state; and, by completing the history of one group of animals, secure the foundation of the whole of biological science. In the Appendix, I have added a few notes re¬ specting points of detail with which I thought it
