6 
CALIFORNIA SEA-SHELLS. 
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 a part of a living creat- 
ure, a hard 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 this protection, but never, while 
life lasts, can it quit its shell and grow a new 
one. 
The members of the sub-kingdom of animals 
to which the shell-bearers belong are called 
mollusks, from the Latin mollis , meaning “soft.” 
Their bodies are indeed soft, since they have no 
internal bones to give them 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 hones, nor, it may be added, 
true brains. 
Mollusks are divided into five classes: CepliaL 
opods, including the Nautilus and Cuttle-fish 
families; Glasteropods or Creepers, such as snails 
and slugs ; Pteropods, little animals living most- 
ly near the surface of the deep sea and swimming 
with wing-sliaped paddles ; Braehiopods or 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 Braehiopods are ar- 
