30 



ECHINODERMATA. 



EOHINODEBMS. 



Starfish, Sea-urchins, and Sea-cucumbers are united into one 

 known as the Echinodermaia. All these animals are 

 marine. They are characterised by their radial symmetry. 

 They have generally a hard calcareous exoskeleton, which may 

 bear calcareous spines. Within the tests are placed the fuUy 

 developed alimentary canal, and the water-vascular and reproduc- 

 tive organs. The starfish, &c., reproduce sexually. The ova 

 produced give rise to curious larval forms, quite unlike the adult. 



The group must be summarily dismissed here, as they are of no 



Fig. 6. — The Common Starfish (f/rosterrMbens). From Nicholson. 



importance to the agriculturist, except in the case of the starfish 

 (fig. 6), which are sometimes employed as manure, the so-called 

 " five-finger " manure, in neighbourhoods near the coast. 



