222 INVERTEBRATE ZOOLOGY 
planarian, 77; tapeworm, 83; mussel, 97; oyster, 102; clam, 110; 
squid, 1382; starfish, 146; Hydra, 161. 
Thorax: the body-division of arthropods following the head; wasp, 2; fly, 
7; grasshopper, 9; caterpillar, 20; spider, 24; crayfish or lobster, 28; 
sow-bug, 46; amphipod, 48; Caprella, 50; larval decapods, 51; cope- 
pod, 53; Daphnia, 56. 
Tibia: the segment of an insect’s leg between the femur and the tarsus; 
wasp, 4; grasshopper, 12; spider, 25. 
Tiedemann’s vesicles: minute diverticula of the ring canal of the star- 
fish, 146. 
Trachea: a respiratory tube; grasshopper, 17; caterpillar, 21; spider, 27. 
Trichocyst: a cyst containing a defensive bristle in the ectosare of Infu- 
soria, 186. 
Trivium : the three rays of an echinoderm opposite to the bivium, 143, 151. 
Trochanter: the segment of an insect’s or a spider’s leg, between the coxa 
and the femur; wasp, 4; grasshopper, 12; spider, 25. 
Trochophore: a larval form common to polychetous annelids. 
Tunic: the outer cuticular covering of tunicates, 135. 
Umbo: the protuberance above the hinge on the shell of a lamellibranch; 
mussel, 89; oyster, 99; clam, 103. 
Ureter: a tube forming the outlet of the kidney; crayfish or lobster, 40; 
mussel, 95; clam, 109; snail, 116. 
Uropod: the sixth swimmeret of the macruran decapod, that which forms 
the swimming tail, 32. 
Uterus : a dilated portion of the oviduct in which the egg or the developing 
animal is detained; planarian, 77; tapeworm, 83. 
Vagina: the terminal division of the female reproductive tract; grass- 
hopper, 16; tapeworm, 83; snail, 120. 
Vas deferens: a duct leading from the testis towards the external opening ; 
grasshopper, 17; crayfish or lobster, 37; crab, 44; copepod, 55; earth- 
worm, 69; planarian, 77; tapeworm, 83; snail, 120; squid, 132. 
Vas efferens: a duct leading from the testis to the vas deferens; planarian, 
77; tapeworm, 83. 
Vegetative organs: those organs which have to do with the processes of 
nutrition, growth, and the expulsion of wastes. 
Vein: a vessel which brings blood towards the heart; crayfish or lobster, 
38; snail, 116; squid, 120. 
Velum : the circular muscular membrane of a medusa, 168, 174, 176. 
