222 INVERTEBRATE ZOOLOGY 



planarian, 77 ; tapeworm, 83 ; mussel, 97 ; oyster, 102 ; clam, 110 ; 

 squid, 132; 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 j 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 ectosarc 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 polychastous 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. 



