GLOSSARY 



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



wasp, 2 ; fly, 7; grasshopper, 10; caterpillar, 20 ; spider, 25 ; crayfish or 



lobster, 31 ; crab, 42 ; sow-bug, 46 ; amphipod, 48, 50 ; larval decapods, 



51; copepod, 53; Daphnia, 56. 

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



starfish, 142 ; sea urchin, 149 ; medusa, 167, 173 ; Gonionemus, 175. 

 Aciculum : a chitinous supporting rod in the parapodia of annelids, 63. 

 Acontia : long threads armed with nettle cells in sea anemones, 178. 

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



body ; mussel, 90 ; oyster, 100 ; clam, 104. 

 Air-sacs : tracheal enlargements in insects, 17. 

 Algae : very simple green plants, 160. 

 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, 163, 169. 

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



dentary apparatus of the sea urchin, 152. 

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



echinoderms, 143, 149, 157. 

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



the starfish, 143. 

 Ambulacral pores : minute openings in the body-wall in the starfish, 143 ; 



in the sea urchin, 150. 

 Ametabolic : larval development without metamorphosis in insects. 

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



146, 153, 157. 

 Anal feelers : paired posterior projections ; centiped, 22 ; sow-bug, 46. 

 Analogous : having a similar function. 

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



wasp, 2 ; beetle, 5 ; fly, 7 ; grasshopper, 9 ; caterpillar, 20 ; centiped, 22 ; 



crayfish or lobster, 29 ; crab, 43 ; sow-bug, 46 ; amphipod, 48 ; copepod, 



53; Daphnia, 56; nauplius, 59. 



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