i8o 



THE BOOK OF NATURE STUDY 



To illustrate Echinoderms, one looks first for the common 

 starfish (Asterias rubens\ a brittle star (such as Ophiothrix fragilis), 



a stray sea-urchin (such 

 as the purple - tipped 

 Echinus miliaris, often 

 half hidden with a 

 burden of little pebbles) . 



FlG. 95. Sun-star (Solaster papposus}. 



FIG. 97. Common starfish (Asterias rubens). M, the madrepore, 

 a perforated plate by which water enters the water-vascular 

 system. 



FIG. 96. Pincushion starfish 

 (Porania pulvillus). 



To watch these 

 move in a basin 

 of water is inter- 

 esting. To watch 

 with a good lens 

 the play of tube- 

 feet and spines 

 and small snap- 

 ping blades on 

 the surface of a 

 sea - urchin just 

 covered with 

 water is to gain 

 an unforgettable 

 impression. 



Similarly, one of 

 the first things to 

 do on the shore is 

 to find a flat stone 



