258 JELLY-FISH, SYAR-FISH, AND SEA-URCHINS. 
nected together so as to compose a series of struc- 
tures not unlike the couples of an ordinary roof. 
These so-called ambulacral plates rest on horizontal 
spine bearing plates, from which other larger plates 
extend upwards to form the sides of the arms. 
In a living Star-fish the tube-feet or pedicels 
already mentioned are seen projecting from each 
side of the ambulacral groove; and, with the excep- 
tion of a few at the tip of each arm, all the tube- 
SSS" EedU0d/X/”"w HAZ = 
- ZZ 
Fig. 35.—The terminal portion of a tube -foot (magnified). 
feet terminate in a well-formed sucker, by means of 
which they can be firmly fixed to a flat surface 
(Fig. 35). 
If we wish to understand the structure and 
mechanism of this locomotor or ambulacral system 
—which, I may observe in passing, is of special. 
interest from the fact that as a mechanism it is 
unique in the animal kingdom—we must resort to 
dissection. We then find that each of the tube-feet 
