SEA-URCHINS AND SEA-CTJOUMBERS. 



289 



SUCKER OF URCHIN. 



knob which was attached to the bottom of the saucer 

 maintains its hold, but the tube has suddenly shrunk up 

 to a sixth part of its 

 former length, ex- 

 changing at the same 

 time its smooth slen- 

 derness and translu- 

 cency for a wrinkled 

 semi-opacity. I push 

 the knob aside with a 

 needle's point and thus 

 destroy its adhesion ; 

 which done, I take 

 up the severed and 

 shrunken sucker, and lay it in a little sea-water in the 

 live-box. 



Under a power of 180 diameters we see that the tube is 

 composed of two series of muscular fibres, the one set 

 running lengthwise, the other transversely or in rings ; 

 the former by their contraction diminishing the length of 

 the tube, the latter diminishing its calibre. The muscular 

 walls are covered with a transparent skin, studded with 

 round orange- coloured spots, perhaps glandular, exactly 

 similar to those we saw on the exterior of the spines and 

 pedicellaria. 



Now, to illustrate the action 

 of these tubular feet, I must 

 again have recourse to the de- 

 nuded shell of a preserved 

 Echinus. Taking this globose 

 empty box in your hand, hold 

 it up against the light, look- 

 ing in at the large orifice, which 

 was once occupied by the 

 mouth: — you see that the 

 whole shell is pierced with 



u 



POKES OP URCHIN. 



