208 INVERTEBRATE ZOOLOGY 
Anterior: at or towards the front end of the body. 
Anus: the posterior opening of the digestive canal. 
Aorta: a large artery leading directly from the heart; spider, 26; snail, 
116; squid, 129. 
Appendage: see Extremity; wasp,1; grasshopper, 12; centiped, 22; spider, 
24; crayfish or lobster, 30; crab, 43; sow-bug, 47; amphipod, 49; Ca- 
prella, 50; larval decapods, 51; copepod, 54; Daphnia, 56; nauplius, 
-59; Nereis, 61, 63: a projection from some part of the body. 
Appendix: a short diverticulum of the intestine, 40. 
Aristotle’s lantern: the dentary apparatus of the sea urchin, 151. 
Artery: a blood vessel carrying blood away from the heart to-the tissues; 
crayfish or lobster, 37,38; Nereis, 64; mussel, 94; clam, 108; snail, 116, 
squid, 127, 129. 
Arthrobranch: a gill attached to the joint between the leg and the body 
in crustaceans, 35. 
Articulate: composed of a series of homologous segments. 
Asexual: reproduction by division or budding and not through the agency 
of the sexes; Bugula, 87; Hydra, 161; hydromedusan, 163, 169 ; sponge, 
183; Paramecium, 187; Vorticella, 190; Euglena, 193; Amoeba, 195. 
Auricle: a chamber of the heart which receives the blood from the veins; 
mussel, 94; oyster, 101; clam, 108; snail, 116. 
Avicularium : a structure shaped like a bird’s head attached to the zocecium 
in Bryozoa, 87. 
Axial organ: a glandular organ in the axial sinus in the starfish, 148; in 
the sea urchin, 154. 
Axial sinus: an elongated sac alongside the stone canal in the starfish, 148; 
in the sea urchin, 154. 
Balancers: the homologues of the metathoracic wings in Diptera, 8. 
Bilateral symmetry : having the right and left sides alike. 
Bivalve: a shell composed of two distinct and equivalent parts or valves; 
mussel, 89; oyster, 99; clam, 103. 
Bivium: the two rays of a starfish or a sea urchin which enclose the 
madreporic plate between them, 142, 151; the two rays on the upper 
side of the holothurian’s body, 155. 
Blastostyle: the reproductive polyp of a campanularian hydroid, 170. 
Body-cavity: an internal space in the body in which lie the viscera. 
Body-wall: the outer portion of the body, which usually bounds the body- 
cavity towards the inside. 
Brachial: relating to the arms. 
