176 GENERAL BIOLOGY 



tentacle. A slender, unsegmented, tactile or prehensile 



organ near the mouth, 

 tergum. The dorsal portion of the exoskeleton of a somite 



in arthropods. 



testis. The male reproductive organ, 

 thorax. The middle of the three divisions of the body of 



an insect. 



tissue. A group of similar cells having a similar function, 

 trachea. The windpipe of vertebrates; a branching air 



tube of insects. 

 trichocyst. A sac or rod-like body in the ectoplasm of 



Paramecium. 

 tubule. A small tube, 

 tympanic membrane. The ear drum or membrane of an 



auditory organ, 

 typhlosole. A longitudinal fold in the intestinal wall of 



annelids, molluscs and certain other animals. 



U 



umbo. One of the lateral prominences just above the hinge 



of a bivalve mollusc shell, 

 ureter. The duct of the kidney, 

 urino-genital. Relating to the urinary and genital organs, 



as urino-genital artery. 



vacuole. A globular space within a cell containing a gas 



or liquid, 

 valve. One of the pieces of the shell of a clam; a flap or 



fold within a cavity which permits the passage of a 



liquid in one direction only. 



