68 A NATURAL HISTORY OF THE SEAS 



thus aiding progression besides keeping foes at a distance. 

 Between the spines and tube feet are thousands of other 

 appendages which can be thrust outwards through the 

 minute port-holes. These extra appendages are generally 

 recognised as being of three well-defined patterns. Some 

 are like pincers mounted on long stalks, and these being 

 very active and mobile quickly seize and destroy any minute 

 creature which might injure the skin. There are also 

 bulb-headed pincers armed with poison glands for use in 

 defence. And thirdly, snake-headed pincers, their jaws 

 armed with fringes of needle-like teeth, which are particu- 

 larly used to hold active prey. The surface of a Sea Urchin, 

 indeed, seen under a lens presents an extraordinary 

 spectacle of restless activity, and an active creature such 

 as a sandhopper falling amongst the forest of swaying 

 tube feet, spines and other appendages is instantly detained 

 and hustled over the creature's surface till it reaches the 

 circular mouth upon the underside. Here it meets with 

 five large grinding " teeth," which are supported by a 

 most complex structure known as " Aristotle's lantern," 

 since it is not unlike an archaic lamp and was first described 

 by the Greek naturalist and philosopher. The " lantern " 

 is composed of some fifty hard limey structures neatly 

 interlocked and combining to form a most effective grinding 

 mill. Certain tube feet near the mouth are employed 

 solely for tasting. 



Sea Urchins abound in most seas and often hollow out 

 vast cavities in the limestone, where they lie embedded for 

 long periods. 



The Sea Egg (Echinus esadentus) is somewhat larger 

 than a man's fist and on the Continent is esteemed as food. 



