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. 



