CONTENTS 



I. INTRODUCTORY 



PAGE 



Materials for the study of Mollusks close at hand — 

 Garden Snail and its shell — Swan Mussel and Common 

 Mussel — Common Sepia or Cuttle — Types of three principal 

 classes of Shell-life ...... 21 



II. THE SHELL AND ITS FORMATION 



Shell/.sA a misnomer — Some INIoUusks without shells — 

 The primitive shell — Importance of the conical form to 

 shore - dwellers — Form of shell determined by habit of 

 MoUusk — Comparisons between the shells of shallow and 

 deep water, rock and sand— The door of the shell— The 

 Oyster a degenerate — Thin shells of pelagic species — Thin- 

 ness of fresh-water shells— Land-snails— Shells of Slugs and 

 Cuttles undeveloped or absent . . . .32 



III. FEEDING AND BREATHING 



Oyster, though headless, has a mouth— Bivalves all 

 tongueless — Cuttles' bird-like beak — The Snail's wonderful 

 tooth-ribbon, and thousands of teeth — Powerful gizzards — 

 Lungs and gills — Air-breathers and water-breathers — The 

 molluscan heart and circulation — Blood mostly colourless . 40 



IV. SEEING, HEARING AND SMELLING 



Sense organs of Mollusks differ from those of higher 

 animals — Decentralisation of sense impressions — Local 

 brains — Nerve-threads, commissures, and ganglia — Eyes and 

 eye-spots — Stalked-eyes, internal eyes, and vanished eyes 

 — Evolution of the molluscan eye — The Argus-eyed Scallops 

 — The Saddle-oyster's sense of hearing— Otocysts and 

 Otoliths — Sense of smell more important than sight or 

 hearing — Whelk's keen scent — Slug's sense of locality— A 

 strange form of nose — Sense of touch acute . . .48 



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