PIBRCED SHELUS AND CHITONS 253 
passed over the animal’s gills, together with any 
waste particles that may be thrown off from the 
various organs. As the shell increases in size, 
some of the holes become closed from the inside, 
while new ones are formed at the edge of the grow- 
ing shell. 
If we look within we shall find the most highly 
colored portion of the shell near the center, where 
the huge muscle which controls the foot has been 
detached. This great foot can cling to a rock 
with surprising force, and the animal must be 
taken unawares if an easy conquest is expected. 
The internal organs are very interesting for dis- 
section, particularly the mouth with its long, rib- 
bon-like tongue, thickly set with flinty hooks, or 
teeth. By means of these teeth the animal rasps 
its vegetable food into fine shreds fit for swallow- 
ing. This lingual ribbon in a good-sized specimen 
is one-fourth of an inch wide, and three inches 
long. 
This species is essentially a southerner. I have 
seen one living specimen at Monterey, but they are 
seldom found so far north. The shell is quite thin, 
and is diversified externally by low spiral ridges 
of a dark and dull color. 
Within, a whole rainbow is condensed in one of 
these magnificent shells, though the shades of 
green are most conspicuous. The coloring of the 
center is particularly fine, resembling a peacock’s 
tail. There are about six open holes near one 
side of the shell, and its length is about the same 
number of inches. 
