This book shows how the careful study of one of the commonest and most insignificant of animals, leads us, step by step, from everyday knowledge to the widest generalizations and the most difficult problems of Zoology; and, indeed, of biological sciences in general. Common and lowly as most may think the crayfish, aptly said Roesel von Rosenhof, it is yet so full of wonders that the greatest naturalist may be puzzled to give a clear account of it. This account of the crayfish was intended to be the means of directing the attention of observers in all parts of the world to the crayfish. And, it has more than succeeded in fulfilling this objective. It should be possible for the reader of this book to complete the history of one group of animals and thereby secure the foundation of the whole of biological sciences.
