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. 
BE ae fava ae 
ae et 
By 
He 
8g Hh: 
Fig. 33.—Tedicellariz (magnified). (From Cassell’s “ Nat. Hist.”’) 
Turning now to the under surface of our Star-fish 
(Fig. 84), we 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, which 
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 emptied 
with fluid. These are used for crawling, 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 structure, we 
