TERMS USED IN DESCRIBING THE STRUCTURE OF ECHINODERMS 



Abo'ral surface : The side opposite the mouth. 



Ambula'cra : Tubular feet used in moving. 



Ambulacral zones : The five areas containing the rows of 

 tube-feet. 



Ampul'lce: Reservoirs or vesicles at the base of the tube-feet. 



Auricula 'ta: The larval stage of holothurians. 



Bipinna'ria or Branchiolaria : The larval stage of starfishes. 



Dorsal surface: The back of the animal, generally, but not 

 necessarily, the upper side. 



Exoskeleton: Outside framework or support, differing from a 

 true skeleton which lies inside the body. 



Interatnbulacral areas : The five areas between the ambula- 

 cral zones. 



Larva: The animal in a stage of development from the time 

 it leaves the egg until it reaches the complete form of the species. 



Madreporic plate : A sieve-like plate of carbonate of lime. 



Oral surface : The side on which the mouth is placed. 



Ossicles : Calcareous plates which cover the body and form the 

 exoskeleton. 



Pedicella'rice : Small spines which have divided ends, like scis- 

 sors or forceps. 



Flu'teus : The larval stage of sea-urchins. 



Po'lian vessels : One to ten sacs arising from the ring-canal. 



Ring-canal : The canal around the mouth. 



Spines : Processes which rise from the surface of the animal. 



Stone-canal : A calcareous tube leading from the madreporic 

 plate to the ring-canal. 



Suckers : Sucking-disks on the ends of the tube-feet. 



Ventral surface: The side opposite the dorsal surface. 



Water-vascular system: A series of canals which conduct 

 water through the animal. 



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