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 



