90 



TRANSACTIONS UYKKPOOL BIOLOGICAL SOCIETY. 



ECHINODERMATA (Star-fishes, &c). 



(Figs. VII. and VIII.) 



Star-fishes, Sand-stars, Brittle-stars, Feather-stars, 

 Sea-urchins and Sea-cucumbers are all characterised by 

 having plates and spicules of lime in the skin which may 

 project from the surface as spines. Hence they are known 

 as " prickly-skinned " animals (Echinodermata). They 

 also have as another important characteristic a remark- 

 able system of tubes containing a watery fluid, parts of 



PlG. VII., Antedon (1 and 2 natural size, 3 magnified about 10 times). 



which can be protruded as suckers for locomotion. These 

 Bucking tubes can be seen acting as feet in star-fishes or 

 Bea-urchins creeping up the glass of an aquarium. In the 

 Echinus shown al 5 (fig. VIII.) the short straight pointed 

 projections are calcareous spines, and the longer flexible 

 bodies are tube-feet, with suckers at their ends. 



