STAR- FISH AND SEA-URCHINS. 



255 



position, and is called the madre]:>oric tubercle 

 (Fig 32, 771). Continuing our examination of the 

 upper surface, we may observe, when we use a lens, 

 a number of small pincer-like organs scattered about 

 between the calcareous nodules, or attached to the 

 spines ; these are known as the pedicellariae. Each 



Fig. 32. Upper surface of a Star-fish {Astropeckn). 

 Hist.") 



(From Cassell's " Nat. 



consists of a stalk serving to support a pair of 

 forceps or pincers, and the whole being provided 

 with muscles, the stalk is able to sway about and 

 the pincers to open and shut (Fig. 33). The entire 

 mechanism is therefore clearly adapted to seizing 

 and holding on to something ; but what it is that 

 these curious orcjans ai-e thus adapted to seize, and 



