Shell Life - An Introduction to the British Mollusca

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PREFACE THE object of this work is much the same as that which led to the writing of its companion volume The Romance of Wild Flowers-to awaken an interest in, and lead to a closer study of, the creatures described. Shells and their makers, of course, aecessitated a different kincl of treatment from that accorded to. the wild flowers but the authors plan of making his readers first acquainted with the outstanding characteristics of the prevailing types of structure as embodied in such familiar forms as the snail, the mussel, and the cuttle, will enable them to follow lliin throughout the further chapters. It is not pretencieci that this volume will enable the reader to determine the exact species of all the native mollusks that Inay come under his notice but it is hoped he may get from it an intelligent idea of the sub- kingdom so far as it is represented in these islands, and may be assisted in discriminating between most of those conlmonly encountered in the woods and lanes, by the pond and stream, or along the seashore. Of the seven hundred and fifty species of Mollusca indigenous in the British Islands and the adjacent seas, no less than six hundred and fifty species have been briefly described in these pages. But it is not as a shell-collectors handbook that the volume is sent forth rather to suggest the consideration of these creatures as living organisms, whose diversity of form and structure has intirnate relation to their mode of life, the persecution of enemies, and other factors in the struggle for existence-though some of us are at times too apt to regard such differences as being dictated by the needs of the classifying naturalist. In accordance with this intention, so far as was compatible with the necessity for producing a volume of handy size, attention has been directed to those habits and external influences that may reasonably be considered to have brought about nodifications of form and colour, protective resemblances, and so forth. A few words may be added as to the system upon which the Genera, Fanlilies, ancl Orders have been grouped see Appendix. In this matter I have mainly followed the plan adopted by the Rev. A. H. Cooke, M.A., in his admirable Molluscs Cambridge Natural History, vol. iii., which is likely to long remain the standard text-book. The reader who desires to enter upon the wider and deeper study of this branch of Nature will thus experience no difficulty in expanding his elenlentary acquaintance wit, h our local. fauna, into a fuller knowledge of the Mollusca of the world Materials for the study of Mollusks close at hand- Garden Snail and its shell-Swan Mussel and Cornnlon Mussel-Common Sepia or Cuttle-Types of three principal classes of Shell-life . . 21 IT. THE SHELL AND ITS FORMATION ShellJish a misnomer-Sonle Mollusks without shells- Tile prinitive shell-Importance of the conical form to shore - dwellers - Pornl of shell determined by habit of Mollusk-Comlarisons between the shells of shallow and deep water, rock and sand--The cloor of the shell-Tle Oyster a degenerate-Thin shells of pelagic species-Thin- ness of fresh-water shells-Land-snails-Sllells of SIugs and Cuttles undeveloped or absent . 32 III. FEEDING AND BREATHING Oyster, thougll headless, has a month-Bivalves all tongueless-Cuttles bird-like beak-The Snails wonderful tooth-ribbon, and thousands of teeth-Yoverfnl gizzards- Lungs and gills-Air-breathers and water-breathers-The nlolluscan heart and circnlation-Blood nlostly colourless . 40 IV...