Book excerpt: "In writing this book about Crayfishes it has not been my intention to compose a zoological monograph on that group of animals ... I have desired, in fact, to show how the careful study of one of the commonest and most insignificant of animals, leads us, step by step, from every-day knowledge to the widest generalizations and most difficult problems of zoology; and indeed, of biological science in general."--The Preface