526 GLOSSARY 



Urethra (ure'thra), the duct which leads from the urinary bladder to the 



exterior of the body. 

 Uropods (u'ro podz), the sixth pair of abdominal appendages of a crustacean. 



Vacuoles (vak'uolz), small cavities in a cell filled with water, gases, or oils. 

 Vagina (vaji'na), the cavity between the uterus and the external genital 



aperture of the female in many animals. 

 Vascular system (vas'kuler), the circulatory system. 

 Vascular tissue (vas'kuler), fluid tissue consisting of cells known as corpuscles 



in a fluid medium, plasma. 

 Vein (van), the larger blood vessels leading to the heart. 



Ventral (ven'tral), side away from the back; literally belly; opposite to dorsal. 

 Villus (vilTis), a fingerlike, vascular process of the internal lining of the small 



intestine. 

 Vitamins (vi'tamins), substances which occur in small amounts in numerous 



foods and are essential regulatory substances for the animal body. 

 Vitelline (vitel'lin), the outer membrane of an egg. 

 Vitreous (vit'reus), glassy in appearance. 

 Viviparous (vi vip'a rus), the retention and development of the egg in the 



mother's body and nourishment of the embryo from the blood of the 



mother. 

 Volant (vo'lant), able to fly. 



Zoogeography (z6 6 je og'ra fi), the study of the geographical distribution of 



animals. 

 Zoology (zo ol'o ji) (animal biology), the study of the science which treats of 



animals. 

 Zygote (zl'got), a fertilized egg, or embryo, after fertilization. 

 Zymogen (zi'mojen), a pre-enzyme; a substance which is produced in a gland 



cell and becomes an enzyme when it is discharged and activated by some 



other substance, perhaps another enzyme. 



