GLOSSARY 



TOTIPOTENT CELL. An undifTerentiated cell 



TRACHEA {pi. TRACHEAE). An air tube; specifically, the air passage from the larynx 

 to the bronchi in vertebrates, or a part of the breathing system in tracheate 

 arthropods. 



TRANSFORMATION OF ENERGY. The process of changing potential energy (energy 

 of configuration or position) into kinetic energy (energy of motion), or the 

 reverse process; in cells, potential energy is stored in the complex chem- 

 ical molecules and released, or transformed, by the disintegration of these into 

 simpler molecules; the transformation of potential into kinetic energy is always 

 accompanied by the production of heat; the activities of organisms are de- 

 pendent on the release of kinetic energy. 



TRIPLOBLASTIC. Having three cell layers, ectoderm, endoderm, and mesoderm, a 

 digestive cavity lined with endoderm, and usually a coelom. CJ. MONOBLASTIC 

 and DIPLOBLASTIC. 



TROPISM. Preferably defined as a forced reaction given to certain stimuli by sessile 

 animals and plants, although often used as a svnonym of taxis. 



TRUE COELOM. See COELOM. 



TYPHLOSOLE. A single, thick, dorsal invagination of the wall of the digestive tract 

 in some invertebrates. CJ. VILLUS. 



ULTRAMICROSCOPIC. Too small to be seen with a light microscope. 



UMBILICAL CORD. A cord containing blood vessels and extending from an embryo 



to its placenta. 

 UMBO {pi UMBONES). A dome-like projection of each valve near the hinges of the 



shells of certain mollusks. 

 UNI-. Combining form, meaning "one." CJ. MULTI-. 

 UNIVERSAL SYMMETRY. Symmetry in any plane passing through a diameter of a 



spherical mass. 

 URINARY. Pertaining to urine. 



URINO-GENITAL. Pertaining to the excretory and genital organs. 

 UTERUS [pi. UTERI). The expanded portion of an oviduct in which zvgotes develop. 



VALVE. Any part of an organism that resembles a hinged door; specifically, thin 



folds that control the direction of flow of blood and lymph, and the parts of 



the shell of pelecypods and brachiopods. 

 VARIATION. The lack of resemblance between the individuals of a species; may or 



may not be heritable. 

 VARIETY. A subdivision of a species. 

 VAS {pi. VASA) See VESSEL. 



VASCULAR. Pertaining to the circulation of fluids. 

 VEGETAL HEMISPHERE. That half of a telolecithal egg which does not contain the 



nucleus and is filled with yolk. CJ. ANIMAL HEMISPHERE. 

 VEGETAL POLE. A point on the surface of an egg opposite the animal pole; one end 



of the egg axis. 

 VEGETATIVE CELL. See METABOLIC CELL. 



VEIN. A blood vessel carrying blood from capillaries toward the heart. CJ. ARTERY. 

 VENTRAL. Pertaining to or situated near the surface away from the back; the lower 



part of an animal or part; opposite to dorsal. 

 VENTRICLE. A hollow part or organ; a cavity; specifically, the ventricle of many 



hearts and the ventricles of the vertebrate brain. 

 VERMES. .See WORM. 



VERNAL. Pertaining to the spring season; as vernal ponds, vernal vegetation. 

 VERTEBRA {pi. VERTEBRAE). One of the ring-like segments composing the vertebral 



column, or backbone. 



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