172 ZOOLOGY. 



' Tibia (Lat. a flute) One of the two bones of the leg.^ 

 Trachea (Gr. tracheia, the windpipe) The tube which connects 



the lungs with the mouth in the air-breathing Vertebrata. 

 Tracheae The air- tubes which ramify the bodies of insects, &c. 

 Trematoda (Gr. trema, a pore) A group of Scolecida to which the 



"liver-fluke" of the sheep belongs. 

 Trilobites (Gr. treis, three ; lobos, a lobe) A group of extinct 



Crustacea found abundantly in the Silurian rocks. They are 



so called because their bodies were composed of three lobes. 

 Tunicata (Lat. tunica, a cloak) A class of Molluscoida which are 



covered with a leathery case. It is also called Ascidioida. 

 Turbellaria (Lat. turbo, I disturb) A group of free-swimming 



JScolecida. They are so called on account of the currents 



produced by the cilia with which their bodies are covered. 



] Ulna (Gr. olene, the elbow) One of the bones of the fore-arm. 

 Umbo (Lat. a boss) The beak of a bivalve shell. 

 Univalve (Lat. unus, one; valvce, folding doors) A shell composed 



of a single piece. Applied to the shells of the Cephalopoda, 



and most of the Gasteropoda. 



Vascular (Lat. vas, a vessel) Belonging to the circulatory 



system. 

 [ Velum (Lat. a veil) The membrane which partly closes the disc 



in the " naked- eyed >J medusce. 

 >- Ventral (Lat. venter, the stomach) Belonging to the lower surface 



of the body. 



Ventricle (Lat. venter) One of the cavities of the heart which 

 receives blood from the auricle, and drives it either to the 

 breathing organs or through the system. 



V Vertebra (Lat. verto, I turn) One of the joints of the back-bone. 

 ^Vertebrata The highest sub-kingdom, characterized by the pos- 

 session of a back-bone. 



Vesicle (Lat. vesica, a bladder) A little sac or bladder. 

 Viviparous (Lat. vivo, I live; pario, I bring forth) Producing 

 the young alive. 



Zooid (Gr. zoon, animal; eidos, form) Applied to the individuals 

 which make up a compound organism. 



Zoophyte (Gr. zoon ; pJmton, a plant) A term sometimes applied 

 to animals which resemble plants, such as the corals, sea- 

 anemones, sponges, &c. 



