JETSAM 349 



we may compare the gelatinous translucent Alcyonidium 

 gclatinosum and the lace-like Membranipora membranacca 

 spreading like a film on the large fronds of seaweed. 



Among the transient components of the jetsam are the 

 delicate shells of the heart-urchin (Echinocardium) , which 

 we find with all the spines rubbed off and beautifully white. 

 The tread of a black-backed gull's foot is enough to break 

 them, and they soon pass into the common denominator 

 of the sand. The purple heart-urchin (Spatangus) is hardly 

 less brittle. It is interesting to find the strong common 

 sea-urchin (Echinus), with all its spines worn off and the 

 balls where their sockets fit on to the shell polished smooth. 

 The masticating mill or lantern which Aristotle saw more 

 than two thousand years ago has fallen out and lies by itself 

 on the sand a puzzling structure to those who do not 

 know what it is, and equally puzzling to those who, knowing 

 what it is, inquire how it came to be. Allied to the sea- 

 urchins are the starfishes, which are often well represented 

 in the jetsam, sometimes occurring in the so-called " comet 

 form " one arm in process of budding off the missing five. 

 For the regenerative capacity of these creatures is extra- 

 ordinarily great a missing arm can be regrown and a 

 surviving arm can regrow all the rest. 



As we search among the jetsam, crowds of " sand- 

 hoppers " spring high into the air, light again on the sand, 

 and are gone. Many of them are so like the sand in colour 

 that it is difficult to see them till they move, and then they 

 burrow with great rapidity. Some of them " feign death," 

 as we say in our ignorance, when they are touched, and 

 will lie absolutely motionless for many minutes. Suddenly 

 the machinery begins to move again, they spring into 

 the air, and we see no more of them. These shore- 

 amphipods are interesting in many ways, but we cannot 

 do more than refer to the important part they play in 



