256 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 



therefore of what use they are in the economy of 

 the animal, has long been a standing puzzle to 

 naturalists. I hope presently to be able to show- 

 that we have succeeded in doing something towards 

 the solution of this puzzle. 



Fig. 33.— redicellariae (magnified). (From Cassell's «• Nat. Hist."; 



Turninir now to the under surface of our Star-fish 

 (Fig. 34), %^e observe that the mouth is situated in 

 the centre of the disc, and that from this mouth as 

 a centre there radiate five grooves or furrows, Avhich 

 severally extend to the tips of each of the five rays. 

 On each side of these grooves there are numerous 

 actively moving membraneous tubes, which may be 

 protruded or retracted by being filled or em[)tied 

 w^ith fluid. These are used for crawding, and I 

 shall therefore call them the feet, or pedicels. 



So much, then, for the external surface of a Star- 

 fish. If, now, we examine the internal stincture, we 



