6 CALIFORNIA SEA-SIIELLS. 



First, then, we must remember that the shell 

 is not an inorganic body, like a stone, nor yet a 

 mere house for an animal to live in, like the nest 

 of a bird ; but that it is apart of a living creat- 

 ure, a hrrd outer layer, belonging to and pro- 

 duced by certain portions of the skin of the an- 

 imal, somewhat as our finger nails are produced 

 by, and really belong to the skin of the fingers. 

 True, the creature of which the shell forms a 

 part oiten has the power to withdraw its soft 

 organs within (his protection, but never, while 

 lite lasts, can it quit its shell and grow a new 

 one. 



The members of the sub-kingdom of animals 

 to which the shell-bean rs belong are called 

 mollusks, from the Latin mollis, meaning "soft." 

 Their bodies are indeed soft, since they have no 

 internal bones to give ihem strength and protec- 

 tion ; their defense in on the outside. Some of 

 them, it is true, have no shells, and in a few of 

 the highest orders, the shell is internal, but none 

 of them have true bones, nor, it may be added, 

 true brains. 



Mollusks are divided into five classes: Cephal- 

 opods, including the Nautilus and Cuttle-fish 

 families; Gasteropods or Creepers, such as snails 

 and slugs; Pteropods, little animals living most- 

 ly near the surface of the deep sea and swimming 

 with wing-shaped paddles ; Brachiopods Gr Lamp- 

 shells, and Lamellibranchs. The shells of the 

 last two classes are composed of two parts or 

 valves, but in internal construction they are very 

 different. The gills of the Brachiopods are ar- 



