172 THE ANIMAL KINGDOM. 



who has not jerked it off for bait or for the variety of 

 colour in its pretty shell, and in so doing noticed a long 

 slender thread attached to its head, and many times longer 

 than its body ? That was the tongue we are looking at. 

 It has, we see, alternate rows of four hooked teeth, and 

 two notched large teeth all the whole length of that thread- 

 like palate, which lies coiled up loosely inside its body, and 

 is thrown forward like a scythe to mow down the lichen 

 upon which it feeds. When the front row of teeth wears 

 away, a second is brought forward, and so the length of the 

 tougue only provides for the little creature's necessities and 

 duration of life. 



PALATE OF CHITON. 



Not so abundant, and very different in formation, is the 

 Chitoiij which we find hidden in crevices of the same rock 

 to which the Limpet clings. The Chiton is the only mol- 

 lusc which has many shells in one. This little creature has 

 eight plates or shells overlapping each other, round the 

 ^external edges of which the breathing organs lie, a row of 

 triangular leaflets vibrating in the water, and resembling 

 gills in structure. The palate we see is long and ribbon- 

 like, with dark-brown teeth on either side, and smaller in 

 the centre ; they are set in a kind of double arch, jointed, 

 and capable of elevation or depression, and used, like those 

 of the Limpet, for vegetable food. 



PALATE OF YELLOW NERITE 



is very pretty, and somewhat like the Periwinkle. The 

 Nerite is that bright-yellow shell so common on our sandy 

 coasts. Children call them " yellow tops." 



PALATE OF NERITINA FLUVIATILIS 



is a fresh water mollusc, found in slow rivers adhering 

 to stones, the shell very prettily chequered with spots or 

 bands of white, brown, purple, or pink. 



PALATE OF LYMN^EA STAGNALIS. 



The three following palates belong to fresh-water 

 molluscs. 



