GLOSSARY 

 Terms which are fully defined in the text are not repeated in this list. 



Aboral surface The surface opposite the one bearing the mouth. 



Ambulacral area The series of skeletal plates bearing the open- 

 ings through which the tube feet protrude. 



Ampullae Small, sac-like reservoirs connected with the tube feet 

 of echinoderms; located inside the body cavity. 



Anterior That part of the body normally directed forward in 

 locomotion. 



Anus The posterior opening of the alimentary canal for the 

 discharge of waste. 



Asexual reproduction Any form of reproduction not involving 

 the functioning of germ cells. 



Asymmetrical Parts of the body arranged irregularly so that 

 no plane could divide the body into equal parts with corre- 

 sponding structures on the two sides of the plane. 



Bilaterally symmetrical Parts of the body evenly disposed on 

 the two sides of a plane which passes through the chief axis 

 of the body. One-half of the body is the mirror image of 

 the other half. 



Bivalve A shell composed of two approximately equal parts 

 hinged one on the other. 



Blastula That stage in the development of a fertilized egg when 

 the cells resulting from cleavage become arranged in a single 

 layer usually surrounding a cavity. 



Budding A method of asexual reproduction in which a small 

 portion of the body gives rise to a new individual. 



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