144 LIFE BY THE SEASHORE. 



between these two extremities there occur five zigzag rows 

 of tube-feet (tf in Fig. 46). These are very different from 

 the long, delicate tubes of a sea-urchin, for they are short, 

 stiff, and can only be very imperfectly retracted. The 

 skeleton, as in all Holothurians, is represented only by 

 deposits of lime in the skin, which are not continuous, and 

 are not at all conspicuous. The internal anatomy we need 

 not consider, but may only remark in passing that most 

 Holothurians have a distressing habit of throwing out 

 portions of their internal organs when attacked or alarmed. 

 In consequence one only rarely gets an intact specimen for 

 dissection; even those which seem uninjured will often be 

 found when opened to have lost some of the viscera. 



tf 



FIG. 46. Sea-cucumber (Cucumaria planci). After Bell, tf, one of the five 

 rows of tube-feet ; te, tentacles surrounding the mouth. 



There is one other Holothurian which occurs not un- 

 commonly all round our coasts, though it is not often seen. 

 If, however, you make that low-tide excursion to a sandy 

 beach which has been recommended as the only way of 

 getting Echinocardium in the living condition, you will 

 probably find among your spoil pink worm-like creatures, 

 which you are not unlikely to describe either as " worms," 

 or as burrowing sea-anemones. They are slender, trans- 

 lucent creatures with an anterior crown of tentacles, and 

 are usually about three inches in length. If you examine 

 the surface of the body with a lens, and also pass your 

 finger over it, you will notice one of the most curious 

 characters of Synapta, as the little creature is called. This 

 is the presence in the skin of little anchors of lime, whose 



