GLOSSARY 



Abdomen: in invertebrates, the posterior body division; in vertebrates 



the ventral area back of the thorax. 

 Aboral: the side of the body opposite the mouth in a radiate animal. 

 Aciculum: a chitinous supporting rod in the parapodia of annelids. 

 Acontia: long threads armed with nettle cells in sea anemones. 

 Adductor muscle : a muscle which draws an organ toward the axis of the 



body. 

 Air sacs : tracheal enlargements in insects. 

 Algae : very simple, green plants. 

 Alimentary tract: the digestive canal, the organ which ingests, digests, and 



absorbs the food. 

 Alternation of generations: the alternate succession of sexual and asexual 



generations in plants and animals. 

 Alveolus: a pyramidal ossicle which supports one of the five teeth in the 



dentary apparatus of the sea urchin. 

 Ambulacral feet: tubular projections with sucker disks at their ends in 



echinoderms. 

 Ambulacral groove: the elongated groove on the oral side of the rays of 



the starfish. 

 Ambulacral pores: minute openings in the body wall in the starfish and 



the sea urchin. 

 Ampulla: a saclike projection of the ambulacral foot in echinoderms. 

 Anal feelers: paired posterior projections. 

 Analogous: having a similar function. 



Antenna: a segmented sensory appendage on the head of arthropods. 

 Anterior: at or toward the front end of the body. 

 Anus : the posterior opening of the digestive canal. 

 Aorta: a large artery leading directly from the heart. 

 Appendage : a projection from some part of the body. 

 Appendix : a short diverticulum of the intestine. 

 Aristotle's lantern: the dentary apparatus of the sea urchin. 

 Artery: a blood vessel carrying blood away from the heart to the tissues. 

 Arthrobranch: a gill attached to the joint between the leg and the body 



in crustaceans. 

 Articulate : composed of a series of homologous segments. 

 Asexual: reproduction by division or budding and not through the agency 



of the sexes. 



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