GLOSSARY 



Ahoral 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. 



AmpuUae — 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. 



Carapace — The shell covering the dorsal and lateral surfaces of 

 head and thorax of a crayfish. 



Caudal — Located at the posterior tip of the abdomen. 



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