GLOSSARY. 193 



Testis. Male genital gland. 



Thorax. The body diviyion of arthropods posterior to the head. 



Tibia. The segment of the leg of an insect that is between the femur and 



tarsus. 

 Trachea. One of the respiratory tubes of certain arthropods. 

 Trichocyst. An infusorian defensive organ. 

 Trivium. The three rays of a starfish that are farthest from the madre- 



poric plate. 

 Trochal disk. The ciliated disk of a rotifer. 



Trochanter. The second segment from the body, of the leg of an insect. 

 Trochophore. An embryo of certain forms, such as the Annelida and 



Mollusca. 

 Tubercle. A small knob-like prominence. 

 Tunic. The outer covering of an ascidian. 

 Tympanum. A membrane of an auditory organ. 

 Typhlosole. A longitudinal ridge in the intestine. 



Umbo. The raised portion of the valve of a clam shell that ends in the 



beak. 

 Umbrella. Applied to the arched portion of a medusa. 

 Uriniferous tube. One of the tubes of a kidney. 

 Uropod. One of the pair of abdominal appendages that, with the telson, 



form the tail-fin of a crustacean. 

 Uterus. A female organ in which young develop. 



Vacuole, contractile. An excretory organ of Protozoa. 



Vacuole, food. A temporary space in Protozoa in which food is digested. 



Vagina. The terminal division of the female reproductive duct. 



Vas deferens. The duct that leads away from the testicle. 



Vas efferens. Sometimes applied to one of the divisions of the male repro- 

 ductive duct of the squid. 



Velum. The circular muscular membrane of a medusa. 



Ventral. Under surface ; belly. 



Ventricle. A division of the heart which forces blood to the body. 



Ventriculus. A division of the alimentary canal of an insect. 



Vestibule. A depression near the mouth in certain Protozoa. See Vorti- 

 cella. 



Vestigial. An organ that remains undeveloped and has no function; 

 rudimentary as applied in anatomy. 



Viscera. Internal organs taken collectively. 



Visceral mass. Applied to the portion of a moUusk that contains stom- 

 ach, intestine, liver, gonads, etc. 

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