SEA-URCHINS. 73 



nevertheless, the same ; and if you could imagine your 

 starfish doubled up into a ball-shaped form, so that 

 the tips of its five rays would meet together at the top 

 of the ball, you would produce a tolerably close like- 

 ness to the sea-urchin's organisation. 



Fig, 20. An Echinus viewed climbing on the glass of an aquarium. 

 The mouth and its five jaws are seen in the centre. 



Included in the starfish class is yet another type 

 of animals known as the sea-cucumbers. These are 

 common enough round our coasts, and are often 

 brought up in the naturalist's dredge. The sea- 

 cucumbers are the " Trepangs " of the Eastern Archi- 

 pelago, and dried " Trepang " is a dietetic luxury of 



