140 



PEDICELLARI^E. 



shell is placed a rounded tubercle, and that the 

 base of the spine is furnished with a hollow 

 socket into which the tubercle fits, so that the 

 spine has perfect facility of movement. The spine 

 is bound to the tubercle by a short tendinous 

 ligament, connecting the centre of each, much as 

 is the case with the larger joints of vertebrate 

 animals. The power of motion is communicated 

 by the membranous covering that envelopes the 

 body during the hfe of the animal. The spines 

 of some foreign species of Echinus are very 

 delicate and sharp, piercing the unwary hand 

 like so many needles. 



Besides all these multiplied means of pro- 

 gression, there are other very tiny organs, which 

 may possibly be used as assistants for the same 

 purpose, or they may possibly perform some office 

 at present unknown. Among the spines there 

 may be seen, with the assistance of a lens, a very 

 great number of little three -headed pincers, 

 standing each upon a flexible footstalk. These 

 are called pedicellaricey and are also found on 

 several of the star-fishes. Some naturalists have 

 regarded them as distinct animals, residing para- 

 sitically upon the Echinus. The Echinus is 

 often boiled and eaten, just like eggs; from 

 which circumstance it is sometimes called the 



