CHITONS. 159 
there are three muscles given off from each piece to 
the succeeding one, one in the line of the back, the 
others at each side. Thus the animal may be con- 
sidered as enveloped in a coat of plate armour, and 
the name of coat-of-mail shell is sometimes applied 
to it by collectors. 
SHELL-PLATES OF CHITON 
The chiton has no projecting head, nor any ten- 
tacles, but a kind of veil that surrounds the mouth; 
the eyes also are wanting. There is a very long 
ribbon-like tongue, armed like that of the limpet, 
with horny teeth. The gills consist of small tri- 
angular leaflets, set in a fringe, which runs along 
the furrow between the mantle and the foot. The 
foot is large, and extends the whole length of the 
animal. 
In the family are comprised two genera, differing 
in the development of the shelly plates. 
