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. 
Ampuil'le: Reservoirs or vesicles at the base of the fue 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. 
Interambulacral 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 : Caleareous plates which cover the body and form the 
exoskeleton. 
Pedicella’rice: Small spines which have divided ends, like scis- 
sors or forceps. 
Plu‘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-vaseular system: A series of canals which conduct 
water through the animal. 
201 
