50 SrAH-FfSIfES AND SEA-URCHINS. 



when you have them in your Aquarium next summer, 

 you will have more interest in watching them and in 

 learning something of their habits of life. 



The figure shows us only the upper side or back. It 

 is studded all over with little knobs, differing in color in 

 different Star- Fishes (No. 39).* These knobs are in 

 fact short spines, and around them are arranged little 

 fork-like projections with two prongs. These forks can 

 open and shut their prongs at will, and may sometimes be 

 seen to catch between them small prey, little shrimps 

 and the like. They probably have some other purpose, 

 but their exact use is not understood. Between the 

 spines are very short hollow tubes, so small that you 

 will not easily distinguish them ; but it is owing to them 

 that the upper side of the Star-Fish has its full and 

 rounded outline. These tubes absorb water, and when 

 a Star- Fish has been left upon the rocks or beach by 

 the retreating tide, its outline becomes comparatively 

 flat ; but as soon as the tide comes up and covers it 

 again, it assumes its rounded shape once more, ex- 

 panding its whole body with the water which fills these 

 minute tubes. If you watch a Star-Fish when just 

 taken from the sea, you may see the water oozing out 

 all over the surface of the back. Near the centre and 

 between two of the arms there is always a round bright- 

 colored spot : in our figure it looks dark. That is a 

 little sieve, through which the water is filtered as it 

 passes into the five principal tubes that run from the 

 stomach to the extremity of each of the arms. 



Now let us turn our Star- Fish over and examine him 

 on the lower side. In the centre you will see a small 



* Pedicellarue. 



