In conclusion, thanks are due to Messrs. A. & C. Black, Messrs. F. Warne & Co., Messrs. Macmillan & Co., Crosby Lockwood & Son, and the Linnean Society for kindly allowing the use of clichés from illustrations in various works published by them.
E. RAY LANKESTER.
TABLE OF CONTENTS.
| THE SHELL GALLERY. | ||
|---|---|---|
| PAGE | ||
| General Notes on Mollusca | [1] | |
| Systematic Arrangement | [7] | |
| Amphineura (Chitons, etc.) | [7] | |
| Gastropoda (Marine Univalves, Land-Snails, etc.) | [9] | |
| Lamellibranchia (Bivalves, Oysters, Cockles, etc.) | [29] | |
| Cephalopoda (Octopus, Cuttlefish, etc.) | [45] | |
| Index to principal Genera of Mollusca | [51] | |
| General Notes on Polyzoa | [54] | |
| Classification | [57] | |
| An account of the Brachiopoda | [74] | |
| Classification | [77] | |
| An account of the Tunicata | [83] | |
| Arrangement | [90] | |
| THE STARFISH GALLERY. | ||
| General account of the Echinoderma | [106] | |
| Crinoidea (Lily Stars, etc.) | [112] | |
| Asteroidea (Starfishes) | [113] | |
| Ophiuroidea (Brittle-Stars) | [114] | |
| Echinoidea (Sea-Urchins) | [114] | |
| Holothurioidea (Sea-Cucumbers) | [115] | |
| Vermes | Platyhelminthes (Tapeworms, etc.) | [116] |
| Nematodes (Round-worms, etc.) | [118] | |
| Annulata (Marine Worms, Earthworms, Leeches) | [122] | |
THE SHELL GALLERY.
GENERAL NOTES ON MOLLUSCA.
The Mollusca constitute one of the principal divisions of the Animal Kingdom, and include such animals as the Octopus, Cuttlefish, Snail, Slug, Whelk, Cockle, and Oyster.
Definition.
They may be characterized as soft, cold-blooded animals, without distinctly marked external division into segments (as in Worms); their cerebral ganglia (the centre of the nervous system) lie above the commencement of the gullet, and are connected with the inferior ganglia by nerve-chords. Their heart consists of two or more chambers, and is situated on the dorsal side of the animal; it drives the blood into spaces between the various organs of the body. Only the Cephalopods possess internal cartilages, but all are without a bony internal skeleton; in the majority this is compensated by an external hardened shell which is formed (secreted) by the outer covering of the animal termed the mantle. |The shell.| The shell may consist of two parts (valves), as in the Oyster, or may be single, as in the Whelk and Limpet, or composed of a series of plates, as in the “Coat-of-mail” shells or Chitons: when well developed it is hardened by a rich deposit of carbonate of lime; but it may be gelatinous, as in Cymbulia, or altogether absent, as in Octopus; it may cover and protect the body, as in the Oyster, lie within the folds of the mantle, as in the Sea-hares (Aplysiidæ), or it may be quite internal, as in the horny “pen” of the Squid. It may be elongated, as in the Elephant Tooth-shell (Dentalium), cup-shaped, as in the Limpet, or spirally coiled, as in the Snail.
Description of the animal.