60 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



term skeleton ; this skeleton consists of a large 

 number of firm calcareous plates closely soldered 



together. Within, or just 

 outside, these plates there 

 runs down every arm, or 

 branch of an arm, a canal 

 which contains water, and 

 from this canal there are 

 given off more or less deli- 

 cate tubes (the so-called 

 tube-feet) which are 

 connected with the canal ; 



Fig-. 22. Pentaorinus Wymlle-fkomsoni. (After Wyville Thomson.) 



all the canals communicate with one another by 

 means of a ring which surrounds the mouth. Owing 

 to the appearance presented by a dried starfish the 

 earlier naturalists spoke of the areas in which these 



