GLOSSARY. 221 



Telson. Hinder division or segment of a crustacean. 



Tentacle. An elongated, unsegmented tactile organ. 



Tentaculocyst. A sense organ of certain medusae. 



Tergum. The dorsal covering of a segment of an arthropod. 



Test. Shell of an echinoid; tunic of an ascidian. 



Testis. Male genital gland. 



Thorax. The body division 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. 



Tro chanter. 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 defer ens. 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. 



