ECHINODERMATA 



21 



the perforations form the ambulacra! areas, the plates between these 

 five areas form the interambulacral areas. The mouth is in the centre 

 of a membranous peristome and is usually provided with a complicated 

 jaw apparatus known as Aristotle's lantern. 



III. Holothuroidea, Fig. 16, sea cucumbers. As the popular 

 name indicates these animals, especially certain species, are distinctly 



FIG. 13. Starfish. xK- 



cucumber-like, having an elongated, spindle form, 'with the anus 

 at one end and the mouth, surrounded by branching ^tentacles at the 

 other. The bony skeleton here consists of small variously shaped 

 plates, usually in such small quantity that the body wall has a soft 

 leathery texture. 



