192 INVERTEBRATE ZOOLOGY 



Anus : the posterior opening of the digestive canal. 



Aorta: a large artery leading directly from the heart; snail. 106 ; squid, 



119. 



Appendage : an extremity ; wasp, 1 ; grasshopper, 10 ; centiped, 20 ; cray- 

 fish or lobster, 26 ; crab, 37 ; sow-bug, 41 ; amphipod, 43 ; Caprella, 



44 ; larval decapods, 45 ; copepod, 48 ; Daphnia, 50 ; nauplius, 53 ; 



Nereis, 55, 57 : a projection from some part of the body. 

 Appendix : a short diverticulum of the intestine, 34. 

 Aristotle's lantern : the dentary apparatus of the sea urchin, 141. 

 Artery: a blood vessel carrying blood away from the heart to the tissues; 



crayfish or lobster, 31, 32 ; Nereis, 58; mussel, 89; clam, 98; snail, 106 ; 



squid, 117, 119. 

 Arthrobranch : a gill attached to the joint between the leg and the body in 



crustaceans, 29. 



Articulate: composed of a series of homologous segments. 

 Asexual : reproduction by division or budding and not through the agency 



of the sexes : Bugula, 81 ; Hydra, 147 ; hydromedusan, 149, 155 ; sponge, 



163; Paramecium, 167; Vorticella, 170; Euglena, 173; Amoeba, 175. 

 Auricle : a chamber of the heart which receives the blood from the veins ; 



mussel, 88; clam, 98; snail, 106. 

 Avicularium : a structure shaped like a bird's head attached to the zooecium 



in Bryozoa, 81. 

 Axial organ: a glandular organ in the axial sinus in the starfish, 138; in 



the sea urchin, 144. 

 Axial sinus: an elongated sac alongside the stone canal in the starfish, 138; 



in the sea urchin, 144. 



Bilateral symmetry: having the right and the left sides alike. 



Bivalve : a shell composed of two distinct and equivalent parts or valves ; 

 mussel, 83 ; clam, 93. 



Bivium: the two rays of a starfish or a sea urchin which enclose the 

 madreporic plate between them, 132, 141. 



Blastostyle: the reproductive polyp of a campanularian hydroid, 156. 



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, 124. 



Branchial : relating to the gills. 



Branchial heart: a lateral heart in the squid, 119. 



Branchiate : bearing gills. 



