204 INVERTEBRATE ZOOLOGY 



Seta: a bristle ; Nereis, 55 ; earthworm, 61. 



Setigerous glands: glands which secrete setae, 67. 



Sexual: reproduction through the agency of the two sexes. 



Shell gland: the kidney of entomostracans ; copepod, 49; Daphnia, 51. 



Siphon: the organ through which water enters or leaves the mantle cavity 



in mollusks and ascidians; mussel, 86; clam, 96; squid, 114; Mol- 



gula, 125. 

 Somite: one of the serial, homologous body-segments which form the 



body of an articulate animal. 



Spermatheca : a sac for the storing of sperm in the female animal, a semi- 

 nal receptacle, 66. 

 Spermatophore : a capsule or mass of spermatozoa ; copepod, 49 ; snail, 111 ; 



squid, 123. 



Spermatozoon: the male sexual cell. 

 Sperm-duct: the vas deferens, 65. 

 Sperm-sac: a sac for the storing of sperm in the male animal, a seminal 



vesicle, 65. 



Sperm-sphere: a mass of spermatozoa in the earthworm, 67. 

 Spicule : a minute calcai - eous or silicious body in sponges and echinoderms. 

 Spiracle : an external opening in the tracheal system ; wasp, 3 ; grass- 

 hopper, 9; caterpillar, 18. 

 Sporosac: a sessile medusoid, one which remains attached to the parent 



hydroid; tubularian, 149; campanularian, 155. 

 Sternite: the ventral portion of an abdominal segment in insects; wasp, 3; 



grasshopper, 8. 

 Sternum: the ventral surface of a thoracic segment in insects; wasp, 3; 



grasshopper, 8. 

 Stigmata: the respiratory openings in the pharyngeal wall in Molgula, 



129. 



Stipes: a division of the maxilla in insects, 11. 

 Stomach: a division of the digestive tract in which digestion goes on; 



crayfish or lobster, 33 ; Bugula, 80 ; mussel, 90; clam, 100; snail, 107; 



squid, 120; Molgula, 127; starfish, 135; sea urchin, 142. 

 Stomach-intestine : a division of the digestive tract in which both digestion 



and absorption go on; grasshopper, 13; caterpillar, 19; Nereis, 58; 



earthworm, 65. 



Stomach pouch: a diverticulum of the stomach; Bugula, 80; squid, 120. 

 Stone canal : a tube joining the madreporic plate with the ring canal in 



echinoderms, 136, 143. 

 Submentum : the basal segment of the labium in insects, 11. 



