vii PHYLUM ECHINODERMATA 171 



sucker-like extremities and, like the tube-feet of the starfish, 

 are the organs of locomotion. A remarkable and charac- 



FlG. 94. — Strongylocentrotus. Entire animal, with the tube-feet extended beyond 

 the ends of the spines. (From Brehm's Thierleben.) 



teristic feature of the internal structure is the presence of a 

 complicated apparatus for mastication known as Aristotle's 

 lantern, consisting of five jaw-like parts, each bearing a 



