THE HAUNTS OF LIFE 63 



Annelid worm on the back of the heart-urchin and watched 

 the spines snap at it. A reddish fluid flowed out from 

 their tips and the worm was dead after a few minutes of 

 violent wriggUng. The minute pedicellarise then separated 

 theroLselves ofE from the test and remained imbedded in 

 the worm. They all broke at the same place, just at the 

 joint between the base of the spine and the test, and some 

 of them were re-grown in about a month. There-growth 

 of these weapons is interesting, and it may be recalled that 

 the common sea-urchin (Echinus) has also the power of 

 regenerating its spines and these only. Because of the 

 globular nature of its body it is not exposed to the risk of 

 losing parts, and we can thus understand why it does not 

 exhibit autotomy and re-growth on the scale illustrated 

 by the starfish and the brittle-star. 



In coimexion with the pedicellariae, it is interesting to 

 notice that a starfish will get the better of a small sea- 

 urchin by applying first one and then another of its arms, 

 to the spiny surface, getting it well nipped by pedicellarise, 

 and then wrenching off a whole crowd. It does this per- 

 sistently over and over again until the sea-urchin is robbed 

 of all its weapons. 



As an illustration of armour the sea-urchin might also 

 serve, but let us turn to Molluscs. Every one who knows 

 the moUuscs of the shore, or has enjoyed a ' beauty-feast ' 

 looking over the cases of shells in a museum, must have 

 been struck with the sohdity of many of these encasements 

 and with the frequently elaborate outgrowths from the 

 surface — ^knobs, shelves, roughnesses, peaks, undulations, 

 and what not. There is a suggestion of sheer exuberance 

 about many of them, and it looks as i£ there were a waste 

 of shell-making material and energy. The explanation is 



