GLOSSARY 221 
Sternum : the ventral surface of the thorax in arthropods; wasp, 3; grass- 
hopper, 10; spider, 25. 
Stigmata: the respiratory openings in the pharyngeal wall in Molgula, 
189. 
Stipes: a division of the maxilla in insects, 13. 
Stomach: a division of the digestive tract in which digestion goes on; 
crayfish or lobster, 36; Bugula, 86; mussel, 96; clam, 110; snail, 117; 
squid, 130; Molgula, 137; starfish, 145; sea urchin, 152; sea cucumber, 
156; sea anemone, 175. 
Stomach-intestine : a division of the digestive tract in which both digestion 
and absorption go on; grasshopper, 15; caterpillar, 21; Nereis, 64; 
earthworm, 71. 
Stomach pouch: a diverticulum of the stomach; Bugula, 86; squid, 181. 
Stone canal: a tube joining the madreporic plate with the ring canal in 
echinoderms, 146, 153, 157. 
Submentum : the basal segment of the labium in insects, 18. 
Subneural gland: a glandular body in ascidians, 138. 
Subumbrella: the oral surface of a medusa, 167, 173, 175. 
Supporting layer: the non-cellular layer between the ectoderm and ento- 
derm in Hydrozoa; Hydra, 160; tubularian, 165; campanularian, 171. 
Swimmeret: an abdominal appendage of a crustacean, a pleopod; crayfish 
or lobster, 32; crab, 43. 
Symbiotic: the living together of two dissimilar organisms, each being 
dependent upon the other, 160. 
Systemic heart: the median heart of the squid, 129. 
Tactile: relating to the sense of touch. : 
Tarsus: the foot of an insect or a spider; wasp, 4; grasshopper, 12; 
spider, 25. 
Telson: the terminal segment of a crustacean, 31. 
Tentacle: an elongated tactile organ; Nereis, 62; Bugula, 86; oyster, 100; 
snail, 114; Molgula, 135; sea cucumber, 155; Hydra, 159; tubularian, 
164; campanularian, 170; Gonionemus, 176; sea anemone, 178. 
Tergite: the dorsal surface of an abdominal segment in insects, 3, 10. 
Tergum: the dorsal surface of a thoracic segment in insects; wasp, 3; 
grasshopper, 10. 
Terminal: towards or at the posterior or the distal end. 
Test: the tunic of the ascidian, 185: the rigid shell of the sea urchin, 150. 
Testis: the male sexual gland; grasshopper, 17; spider, 27; crayfish or 
lobster, 87; crab, 44; copepod, 55 ; Daphnia, 58; earthworm, 71; 
