SEA-URCHINS AND SEA-CUCUMBERS 



327- - 



We see, tlien, extending from various points of the 

 shelly case of the Urchin, and reaching to twice or thrice 

 the length of the longest spines, slender pellucid tubes, 

 slightly tapering toward their free extremity, which then 

 abruptly dilate into a hemispherical knob, with a flat end. 

 These very delicate organs are extended or contracted at 

 the will of the animal, turned in every direction, waved 

 hither and thither, and evidently have the faculty of ad- 

 hering very firmly by their dilated tips to any object to 

 which they are applied. 



So much we can discern as we watch the creature dis- 



SUCKER OF URCHIN. 



PORES OF URCHIN. 



porting in this vessel of water; but we will now endeavor 

 to learn a little more about its structure and economy. 

 Selecting for this purpose a sucker which is extended to 

 great length, I snip it across with a pair of sharp scissors, 

 as near the base as I can. Mark the result. The terminal 

 knob which was attached to the bottom of the saucer main- 

 tains its hold; but the tube" has suddenly shrunk up to a 

 sixth part of its former length, exchanging at the same 

 time its smooth slenderness and translucency for a corru- 

 gated semi-opacity. I push the knob aside with a needle's 

 point and thus destroy its adhesion; which done, I take 



