rock in some localities has been hollowed out to a considerable depth by 

 the continuous dwelling thereon of the limpet. If the surface of the 

 rock is uneven, the shell grows in such a manner as to fit these inequal- 

 ities. The large foot is very strong, and it is almost impossible to dis- 

 lodge it from the rock when the animal becomes alarmed and is aware 

 that danger is near. While grazing along the sides of a rock covered 

 with fine seaweed, it will leave a track like a worm, and will clear 

 off quite an area in a short space of time. This track is made by the 

 radula, which is very long and is thrust out and loaded with food, which 

 it carries to the mouth. When at rest, it is coiled like a watchspring. 



In the limpet we find a departure from the general form in both 

 animal and shell, both being bilaterally symmetrical ; that is, having the 

 two sides alike. In the majority of snails, the body is twisted in the 

 form of a spiral, making one side different from the other, and causing 

 the organs of one side to become atrophied, or made very much smaller. 

 In the limpets the organs are paired, as they are supposed to have been 

 in the ancestors of the living mollusks. On the British coast, the limpet 

 is used as an article of food, and primitive man not only ate the 

 mollusks but formed a necklace by stringing the shells together. There 

 are several hundred species of limpet-like shells, and they are found 

 in all parts of the world, though generally on rocky shores. 



A family of shells closely related to the limpets is the Fissurellidce, 

 or keyhole limpet, distinguished from the last family by having a slit, 

 or foramen, in the apex of the shell, through which the waste products 

 of digestion are discharged. This slit resembles a keyhole, and for this 

 reason they are called keyhole limpets. The shells of Fissurella are 

 generally rougher than those of the Patella, and they live, as a rule, 

 in warm seas. In habits, the keyhole limpet resembles its relative the 

 limpet, living in one rocky place and making excursions for food. 

 In the young shell the spire is without a perforation, this appearing 

 as the shell increases in age. There are over a hundred species of this 

 family, several handsome species of which inhabit Florida and the West 

 Indies. 



The Haliotis, or abalone shells, abound in many parts of the world, 

 and are widely known for their beauty. The largest and finest shells 

 live on the coast of California, where they attain a length of ten inches. 

 The shells are flat, though made in the form of a spiral, and are perfor- 

 ated near the edge of the last whorl, which is many times the size of all 

 the rest combined. Through these holes the water from the gills, 

 together with the waste products of the animal, pour out. As the shell 

 increases in size, the old holes are filled up and new ones are formed. 



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