vi CONTENTS 



CHAPTER VII 



BACKBONELESS ANIMALS (INVERTEBRATA). STRUCTURE AND 

 CLASSIFICATION OF NEMERTINES AND MOLLUSCS 



Page 



Distinctive Characters of Higher Invertebrates as compared with Vertebrates - 302 

 Main Groups or Phyla of the Invertebrates - 304 



NEMERTINES (NEMERTEA) 

 Structure of a Typical Nemertine 305 



MOLLUSCS (MOLLUSCA) 



Structure of the Ormer or Sea-Ear (Haliotis tuberculata), taken as a Type 307 



Essential Characters of Molluscs - 311 



Class i. HEAD-FOOTED MOLLUSCS (Cephalopoda) - - - 311 



Structure of the Common Cuttle-Fish (Sepia officinalis), taken as a Type - 311 



Sub-Class I. CUTTLE-FiSHES AND OCTOPI (Dibranchiata) 314 



Sub-Class II. PEARLY NAUTILUS (Tetrabranchiata) - 316 



Class 2. SNAILS AND SLUGS (Gastropoda) 317 



Sub-Class i. STREPTONEURA OR FORE-GILLED SNAILS (Prosobranchia) 318 



Order i. COMB-GILLED SNAILS (Ctenobranchia) - 318 



Structure of the Periwinkle (Littorina littorea) and Purple-Shell (Purpura 



lapillus), taken as Types. 



Whelks, Mitre-Shells, Volutes, Olive-Shells, Harp-Shells, Cone-Shells, 

 Turret-Shells, Wing-Shells, Helmet-Shells, and Cowries; Heteropods. 



Order 2. SHIELD-GILLED SNAILS (Aspidobranchia) - 322 

 Trochidas, Ormers, Limpets. 



Sub-Class 2. EUTHYNEURA - - 324 



Order i. HIND-GILLED SNAILS (Opisthobranchia) 324 



(i) Tectibranchs (Bubble-Shells, Sea-Hares, Wing-footed Snails or 

 Pteropods) (2) Nudibranchs (Sea-Slugs). 



Order 2. LUNG SNAILS (Pulmonata) 326 



Structure of the Garden Snail (Helix aspersa), taken as a Type - 326 



Land Slugs, Fresh-water Pulmonates. 



Class 3. BIVALVE MOLLUSCS (Lamellibranchia or Pelecypoda) - 328 



Structure of Fresh-water Mussels (Unio and Anodonta), taken as Types 328 

 (i) Cockles (2) Gapers (3) Razor-shells (4) Rock-borers (5) Sea Mussels 



(6) Ark-Shells (7) Scallops (8) Oysters (9) Nucula Family 333 



Class 4. TUSK-SHELLS (Scaphopoda) 338 



Structure of the Common Tusk-Shell (Dentalium vulgare). 



Class 5. PROTO-MOLLUSCS (Amphineura) 339 



Mail-Shells (Chitons), Worm-like forms (Neomenia, Proneomenia, Chaeto- 

 derma). 



CHAPTER VIII 



STRUCTURE AND CLASSIFICATION OF JOINTED-LIMBED 

 ANIMALS (ARTHROPODA) 



Essential Characters. Subdivisions - - 342 



