140 MARVELS OF FISH LIFE 



ing how often negatives taken at totally different times 

 and places will piece together to illustrate the life of 

 any particular animal — or you may adopt the more 

 interesting method of devoting your attention to some 

 individual form of life, say, for example, the sea-urchin. 



Sea-urchins are to be found everywhere, but I have 

 never seen the common sea-urchin (Echinus esculentus) 

 in greater numbers, more beautiful in colour, or larger 

 in size, than on the old breakwater at Port Erin. Here 

 the sea is generally clear, and on a still day these urchins 

 can be watched as easily under ten feet of water, as 

 when they are only a foot or two below the surface. 



It may seem strange that the sea-urchin should be 

 classified by zoologists with star-fishes, brittle stars, 

 and sea-cucumbers, but close examination will show 

 that in their structure they are very similar. 



The common star-fish (Asterias rubens) with which 

 most of us are quite familiar, has five fingers, and in a 

 groove along the under-surface of each finger are 

 numerous semi-transparent structures known as tube- 

 feet, each of which is capable of expansion and con- 

 traction and terminates in a sucker. By means of 

 these tube-feet the star-fish attaches itself to rocks, 

 and also moves about. If an attempt is made to pick 

 a star-fish off a rock under the water, considerable 

 force may have to be exerted, and many of the tube- 

 feet will be torn away. 



In the sea-urchin nature has bent up these five 

 fingers and made them meet on the top. The flat 



