THE
COMMON SHELLS
OF
THE SEA-SHORE.
CHAPTER I.
Introduction—semi-molluscs—the tunicates—why so called—general structure of the tunicates—ascidians—their appearance and locality—the botryllus, and its structure—where it is to be found—the perophoria, its general appearance—the Ascidiadæ, or sea-squirts: why so called—curious ideas of the sailors—practical jokes—the siphons—anatomical structure of an ascidian—how to dissect the animals—eggs and buds—the Cynthia, its appearance and locality—Ascidia mentula, the largest known species; its shape and size—the Pelonea—origin of its name—habits of the Pelonea—modification of structure—zoological value of the Pelonea.
Although this work is entitled "The Common Shells of the Sea-Shore," it necessarily embraces several species of molluscs which do not secrete shells at all, and which are clothed simply by their membrane, or by a tough, leathery envelope. These animals must be introduced, because a knowledge of their structure is needed, in order that the shell-making molluscs may be properly understood; but they will only be mentioned for that purpose, and any description of them will be curtailed as far as possible. We will begin at the beginning.
There is a large group of molluscs which are appropriately called Tunicata, because their bodies are wrapped in a tunic, or envelope, instead of being protected by a shell. This tunic has always an inlet and an outlet,
B
