THE AUSTRALIAN MUSEUM MAGAZINE. 



105 



read a book. But the light gives out no 

 heat, and the most delicate temperature 

 recorders are unaffected by it. Nor is 

 it produced by any kind of combustion, 

 for oxygen gas, the greatest of all sup- 

 porters of combustion, has no effect on 

 it. 



SEA-URCfllXS. 



Sea-urchins will be found in hollows 

 on the undersides of the rocks at dead 

 low tide. They are curious animals, 

 living in a shell case or test, which, 

 when thrown up t)n the shore denuded of 

 spines, is often called a sea-egg. This 

 shell is composed of limestone and is not 

 all in one piece; several hundreds of 

 pieces go to the making of even the 



-'S' 



Corona of sea urchin (Toxocidaris 

 erythrogrammus) . 



The corona or shell with the spines removed. 

 The bands of tubercles mark the points of 

 attachment of the spines, and the perforations 

 intermingled with the smaller of these form the 

 openings through which the feet protrude. 

 Photo. — A. Musgrave. 



smallest. The shell is quite thin, and 

 its growth is really marvellous. When 

 quite young, the animal is less than the 

 size of a marble, and it has to grow. 

 Its case has to hold it and must there- 

 fore be made lai'ger, but the animal is 

 inside it; how can it make its case 

 larger from the inside f The secret lies 

 in the fact that the case is not, all in 

 one piece. All the pieces fit most ac- 

 curately, but each is covered with a 

 layer of living tissue which passes be- 

 tween the joints and which can secrete 



lime from the sea water. In this way 

 the various pieces are extended at the 

 edges, all still fitting tightly, and so the 

 case is enlarged though the builder in- 

 side never sees what he is doing. 



The spines of a sea-urchin are all mov- 

 able and present a dangerous opposition 

 to an attacker. They are often very 

 numerous; in a large jiurple urchin com- 

 mon on our coast I once calculated the 

 number to be about 1,100. 



The sea-urchin is also well provided 

 with feet. They do not always pro- 

 ject, but are pushed out when required. 

 They consist of little, white, hollow 

 tubes with a sucking disc at the end, 

 and are provided with fine muscles. 

 When the animal wishes to walk, it 

 forces the tubes through holes in its 

 case by fiUing them with water from 

 the inside as if from a force pump, 

 and when they are full the muscles take 

 control and the animal walks. 



The mouth of the sea-urchin consists 

 of five jaw-like parts each bearing a 

 powerful tooth. The teeth project 

 through the central opening under the 

 shell, and can exert enormous strength. 

 It is largely with these teeth that the 

 urchin cuts out the hollow in the rock 

 where it lives. 



STARFISHES. 



The general design of all starfishes is 

 based on the same foundation, that of 

 rays projecting from a central disc. 

 They are remarkably 'leggy" creatures, 

 as you will see if you turn one over 

 smartly on its back. The little white 

 legs will be seen waving wildly in the 

 air. In construction they are much the 

 same as the tube feet of the sea urchin. 



Each ray of a stai-fish has a small 

 primitive eye spot at the end of it, and 

 just above it is a small projection like 

 a tentacle which is used as an organ of 

 smell, so that the starfish is well pro- 

 vided witli noses. A very beautiful star- 

 fish is found on the rocks exposed to 

 tlie battering of the ocean, and I am 

 sure that the colouring on its back must 

 have inspired the first artist in Satsuma 

 ware. 



A starfisli is a very remarkable ani- 

 mal in its method of feeding. It fre- 



