SEA URCHINS MATERIAL AND DEVELOPMENT. 79 



while one will cost but a penny or tAvo, another, to all 

 appearance exactly like it, can be sold for its weight in 

 silver. 



Fig. 7. SYNAPTA. 



In the British Museum there is a fine collection of the 

 various qualities of Trepang. In these creatures the 

 body is much elongated, and, instead of being covered 

 with calcareous plates and spines, has no real spines, and 



