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. 
Algz: 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, 148, 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, 48; sow-bug, 46; amphipod, 48; copepod, 
538; Daphnia, 56; nauplius, 59. 
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