206 INVERTEBRATE ZOOLOGY 



Trochanter: the segment of an insect's leg, between the coxa and the 



femur; wasp, 4; grasshopper, 10. 

 Trochophore : a larval form common to trochozoa. 

 Tunic: the outer cuticular covering of tunicates, 125. 



Umbo : the protuberance above the hinge on the shell of a lamellibranch ; 



mussel, 83; clam, 93. 

 Ureter: a tube forming the outlet of the kidney; crayfish or lobster, 34 ; 



mussel, 89; clam, 99; snail, 106. 

 Uropod : the sixth swimmeret of the macruran decapod, that which forms 



the swimming tail, 26. 

 Uterus : a dilated portion of the oviduct in which the egg or the developing 



animal is detained; planarian, 71; tapeworm, 76. 



Vagina : the terminal division of the female reproductive tract ; grass- 

 hopper, 14; tapeworm, 76; snail, 110. 



Vas deferens : a duct leading from the testis towards the external opening ; 

 grasshopper, 15; crayfish or lobster, 33 ; crab, 38 ; copepod, 49 ; earth- 

 worm, 63; planarian, 71; tapeworm, 76; snail, 110; squid, 122. 



Vas efferens: a duct leading from the testis to the vas deferens; planarian, 

 71; tapeworm, 77. 



Vegetative organs: those organs which have to do w r ith the processes of 

 nutrition, growth, and the expulsion of wastes. 



Vein : a vessel which brings blood towards the heart ; crayfish or lobster, 

 .32; snail, 106; squid, 119. 



Velum: the circular muscular membrane of a medusa, 154, 160. 



Ventral: on or towards the underside of an animal. 



Ventricle : a chamber of the heart from which blood is sent over the body ; 

 mussel, 88; clam, 98; snail, 106. 



Vesicula seminalis: a sperm-sac in the male animal; squid, 122. 



Viscera: the organs within the body-cavities. 



Visceral mass : the compact group of organs comprising the principal 

 viscera in mollusks ; mussel, 84; clam, 94; snail, 103; squid, 115. 



Wing-covers: the first pair of wings of a beetle, the elytra, 5. 

 Yolk glands: planarian, 71; tapeworm, 77. 



Zoea: a larval form of the crab and of certain other crustaceans, 45, 

 Zocecium: the outer cuticular covering of a bryozoan, 79. 



