470 



Marvels of the Universe 



the same time you will become aware of the presence of active living bodies among the spines 

 that at first you will regard — quite reasonably — as little worms with jaws like the beak of a bird, 

 except that some have three bills instead of two. These remarkable bodies were formerly con- 

 sidered as parasites, and named and classified as a distinct group of animals. They are really 

 part of the Urchin organization, and apparently modified spines, for they have a solid, stony base, 

 and a pliant, fleshy " neck " between it and the beak. The probability is that when you touch 

 the delicate flesh of the Urchin that covers its box your instrument will be in the neighbourhood 

 of one of these bodies ; if so, it will turn in the direction of the annoyance, snapping its beak and 

 probably taking a grip. Their principal purpose is apparently to keep offensive refuse from 

 accumulating between the spines, for they may be seen to pick up such particles and convey them 

 as far as their length permits, and so handing on the duty to others. But they also serve as 

 weapons of defence, for they have been observed to repulse Star-fishes by biting their sucker-feet. 



I'hot'i by'] [//. /. Hhepstoiif. 



TWO JAPANESE URCHINS. 



These are in life covered with bristles, similar to those of the Heart Urchin. The pores for the water-tubes are all on 

 the upper surface and form the outlines of a flower's petals. 



The Urchin has sucker-feet also. The minute perforations in the five-sided plates of which 

 the box is built up give e.xit to little fleshy tubes, each ending in a sucker. It is by means of these 

 apparently weak but really powerful suckers that the Urchin climbs up rocks or travels over the 

 sea-bottom in search of food. The tubes are filled with water and the suckers are worked by water 

 power ; a special system of water-vessels inside the box supplying the necessary pressure. In our 

 Common Sea-Urchin these tubes extend from the base to the summit, so that by their aid, should 

 the Urchin get turned upside down, it can easily right itself again. Some of its relatives, however, 

 are not so liberally provided. The Heart-Urchin shown on page 473, for example, has them only 

 on the upper and under surfaces, not down the sides. 



Certain of these organs, distinguished by ending in a clear round head, are noticeable on the 

 upper surface of the Urchin. The comparative robustness of these heads is due to the fact that 

 each of the three jaws bears on its exterior a transparent pouch, filled with liquid, from which two 

 tubes run nearly to the tip of the jaw. The liquid in the pouch is poison. When the jaws are closed 



