CHAPTER LV. 

 ECHINODERMATA ANNULOSA ENTOZOA INSECTA. 



SEA-URCHINS STAR-FISHES FEATHERY STARS SEA-CUCUMBERS WORMS 



LEECHES ROTIFERS TAPE WORMS INSECTS. 



THE ECHINODERMATA or spiny-skinned, are most commonly represented 

 by the sea-urchins and star-fishes of our coasts. In some of the classes 

 locomotion is performed by means of these spines or prickles, which serve as 

 legs. In others, movement is carried on by suckers and tubes as in the 

 star-fishes, these tubes being also the means whereby the animal obtains its 

 food. 



They have a digestive system, and possess a curiously horny skin even- 

 when spines are absent. The mouth is in the centre. We give an illus- 

 tration of the sea-urchin, and of a section of a .spine, which is a beautiful 

 object when seen under the microscope, for these spines can be made quite 



Fig. 838. Sea-urchin (echinus), with and without spines. 



transparent when cut across and ground. The shelly covering is porous, 

 and as the animal grows the shell is added to at the edges. Underneath 

 will be found the mouth, which has teeth fitted for devouring the small 

 Crustacea. These sea-urchins abound, and their porous shells may be picked 

 up frequently after a storm. 



The star-fishes are well known to all searchers amongst the rocks and 

 those who study the shore, and are often taken home for an aquarium. 

 They are very voracious, however, and when one is examined in a glass of 

 sea-water, the observer will detect many suckers protruding from each of 

 the rays. It is by means of these suckers, which are put forth from 

 innumerable little holes called " ambulacral apertures," that the star-fish 

 makes his way up the rocks and along the ocean bed. The stomach of the 

 star-fish is extensive, and situated in the centre of the rays wherein is a 

 digestive apparatus. The rays are composed of detached but beautifully 



