56 ECHINODERMATA. 



and Sea-cucumbers, suckers are the proper organs 

 of motion. If we put an Urchin into a glass of 

 sea-water, we presently perceive a multitude of 

 slender, pellucid, fleshy threads pushed out from its 

 surface, each tipped with a little knob. We see 

 these waving to and fro, until one after another 

 comes in contact with the glass, to which the knob 

 adheres, as a dilated circular plate ; and that with 

 such force that the animal is able, by the common 

 power of many of these " sucker-feet," slowly to 

 drag itself along, others being ready every instant 

 to take fresh hold, and assist the pulling, in the 

 course of the progression. Under the microscope 

 the tip is found to be occupied by a round cal- 

 careous plate ; and the muscular flesh which 

 surrounds it being pressed close to the surface 

 of the glass, a vacuum is formed, on the principle 

 of a cupping-glass, which resists considerable 

 force, until the creature relaxes its muscular con- 

 traction. When they are no longer wanted in 

 action, they are withdrawn and disappear ; and if 

 we examine the animal in a dry state, after rubbing 

 off the investing spines, we shall see what has 

 become of them : they were withdrawn, at least 

 with the exception of the terminal knob, into the 

 interior of the shell, through those minute holes 

 which I just now spoke of as running in five 

 double series down the sides of the animal. 



According to Professor Forbes there are, in a 

 moderate-sized Urchin, sixty-two rows of pores in 

 each of the ten series or "avenues;" and as there 

 are three pairs of pores in each row, the total num- 

 ber of pores is 3,720 ; but as each sucker occupies 

 a pair of pores, the number of suckers is I860.* 



* " British Starfishes," p. 152. 



