404 PRINCIPLES OF ANIAfAL BIOLOGY 



Tissue. A group of cells of similar structure forming a contiiuious mass or 



layer. 

 a-tocopherol (aV Ja to kof er ole). Vitamin E, the antisterility vitamin of rats. 

 Tonsil. A glandular organ at the side of the throat. 

 Trachea {tra' ke a). The tube conveying air to and from the lungs in vertebrates. 



Also an air tube in insects and some other invertebrates. 

 Tracheal gills. Threadlike or leaflike projections in which tracheae have their l)egii^- 



ning in certain aquatic insect larvae. 

 Trachelocerca {tra' ke lo ser' ka). A genus of ciliated protozoa. 

 Transverse process. One of a pair of projections at the sides of a vertebra in most 



vertebrate animals. 

 Trematoda {trem' a to' da). A class of Platyhelminthes, parasitic flatworms with 



suckers and without cilia. 

 Triassic. Of the earliest Mesozoic time. 

 Triceratops {tri ser' a tops)^ A genus of three-horned dinosaurs of late Cretaceous 



time in western North America. 

 Trichinella (trik' i neV la). A genus of parasitic roundworms, the cause of the disease 



tricliinosis. 

 Triclad. Having the digestive tract divided into three branches; said of an order of 



flatworms. 

 Trilobite (tri' lo bite). A primitive crustacean of Paleozoic time, having the body 



partially divided by longitudinal grooves into three lobes. 

 Trilophodon {tri lof o don). An extinct genus of animals from the Miocene of several 



continents; related to the elephants. 

 Trionychidae (tri' o nik' i dee). A family of turtles. 



Triploblastic (trip' lo bias' tik). Composed of three fundamental layers of cells. 

 Triturus. A genus of salamanders. 

 Trochophore. A form of free-swimming larva characteristic of many worms, mol- 



lusks, and rotifers. 

 Trypsin. A protein-splitting enzyme produced by the pancreas. 

 Trypsinogen (trip sin' o jen). The inactive substance from which the enzyme trypsin 



is produced. 

 Tube feet. Tubular protusions from the arms of echinoderms, which serve as organs 



of locomotion. 

 Tubercula pubertatis (tu ber' ku la pii' ber ta' lis). Two thick glandular ridges on the 



clitellum of an earthworm near the ventral surface. 

 Tuberculate. Bearing cusps or conical prominences; said of teeth. 

 Tubular gland. A gland whose lumen is of about uniform bore throughout. 

 Tunicata (tu' ni ka' ta). A subphylum of Chordata, including the sea squirts, s(>a 



pork, salpas, etc. For definition see Chap. 19. 

 Turbellaria (tur' bcl la' ri a). A class of Platyhelminthes, ciliated flatworms leading 



a free existence. 

 Type. In systematic zoology, an individual or group which is formally held to Im> 



typical of the species or larger group to which it belongs; as, the type specimen of 



a species, the type species of a genus, or the type geims of a family. 

 Typhlosole (tif lo sole). A ridge resulting from the infolding of the dorsal intestinal 



wall of the earthworm. 



Ulna. The bone of the little-finger side of the forearm in Anipliibia and tlu^ higher 



vertebrates. 

 Umbilical cord. A ropelike cord in which blood vessels pass bet\v«!en an embryo and 



the placenta in viviparous mammals. 



