86 A NATURAL HISTORY OF THE SEAS 



none of our twelve or more native kinds exceed an inch 

 in length. Like many of the higher molluscs, Chitons 

 have a long ribbonlike tongue with many thousands of 

 " teeth " arranged upon it in rows. This organ is used 

 as a file and can be employed to rasp away vegetation, 

 or even drill a hole in some hard substance. 



Some near relations of the Chitons known as the 

 Aplacophora are wormlike creatures which have no trace 

 of a shell and live amongst mud, a few apparently attacking 

 corals and hydroids. 



Class 2. The Gastropods. These include many 

 species whose names are household words. As the term 

 " gastropod " implies the animals have the foot in the 

 gastric region — a broad muscular expanse on the under- 

 surface of the body and by means of which the creature 

 glides or scrambles at varying rates. The animal usually 

 carries a shell, into which it can retreat at will, and often 

 there is a horny or stony cap attached to the hinder portion 

 of the foot which automatically closes the mouth of the 

 shell against intruders. There is usually present a pair of 

 well-defined eyes, two or more tactile organs — tentacles, 

 and the already-mentioned tongue. 



The Limpet (Patella) is familiar to all. It is of world-wide 

 distribution and is usually found between tide marks. 

 The animal clings to its anchorage with a persistence 

 which has made it a by-word for tenacity. Experiments 

 with a spring balance show that a limpet with a shell 

 one and a half inches in diameter has a resistance of 70 lbs., 

 and thus the adhesive power of some tropical forms 

 which reach a foot across may well be imagined. Limpets 



