GLOSSARY 



Abdomen : the most posterior of the three body-divisions in arthropods ; 



wasp, 2 ; grasshopper, 7 ; caterpillar, 18 ; crayfish or lobster, 22 ; 



crab, 36; sow-bug, 40; amphipod, 42, 44; larval decapods, 45; 



copepod, 47; Daphnia, 50, 

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



starfish, 132 ; sea urchin, 139; medusa, 153, 159. 



Aciculum : a chitinous supporting rod in the parapodia of annelids, 57. 

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



body ; mussel, 84 ; clam, 94. 

 Air-sacs : tracheal enlargements in insects, 13. 

 Algae : very simple green plants, 146. 

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



and absorbs the food; see digestive system in Index. 

 Alternation of generations : the alternate succession of sexual and asexual 



generations in hydromedusans, 149, 155. 

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



dentary apparatus of the sea urchin, 142. 

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



echinoderms, 133, 139. 

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



starfish, 133. 

 Ambulacral pores : minute openings in the body-wall in the starfish, 133 ; 



in the sea urchin, 140. 



Ametabolic : larval development without metamorphosis in insects. 

 Ampulla : a sac-like projection of the ambulacral foot in echinoderms, 



136, 143. 



Anal feelers : paired posterior projections ; centiped, 20 ; sow-bug, 40. 

 Analogous : having a similar function. 

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



wasp, 2 ; beetle, 5 ; grasshopper, 7 ; caterpillar, 1 8 ; centiped, 20 ; 



crayfish or lobster, 23 ; crab, 37 ; sow-bug, 40 ; amphipod, 42 ; cope- 

 pod, 47 ; Daphnia, 50 ; nauplius, 53. 

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



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