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, 

 139. 



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, 131. 



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, 13. 



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, 135 : the rigid shell of the sea urchin, 150. 

 Testis: the male sexual gland; grasshopper, 17; spider, 27; crayfish or 



lobster, 37 ; crab, 44 ; copepod, 55 ; Daphnia, 58 ; earthworm, 71 ; 



