GLOSSARY 613 



Vesalius (ve sa' II us), Andreas. Belgian anatomist; 1514-1564. 



vesicle (vgs' I k'l). A small sac, especially one filled with fluid. 



vestigial (v6s tij' I al). Existing only as a remnant of a former condition. 



villus (vll' tis). One of numerous, minute, vascular, finger-like projections on a 

 surface, as on the surface of the small intestine or of the chorion in mammals. 



Virchow (fer' k5), Rudolph. German pathologist; 1821-1902. 



virus (vi' rtis). Consists of ultramicroscopic particles having the power of growth 

 and reproduction. Certain kinds are thought to cause diseases in man, such as 

 measles and smallpox, and many diseases in other animals and plants. 



viscera (vis' er a). The soft organs contained in a coelom; adj., visceral; the appli- 

 cation is often extended to cover the whole length of the alimentary canal, as 

 in the case of pharyngeal arches and the visceral portion of the skull. 



vision. The perception of an image derived from nervous impulses originating in an 

 eye; a mental picture of objects external to the body. 



vitalism (vi' tal Iz'm). The conception of a vital force, neither chemical nor physical, 

 back of all life phenomena; adj., vitalistic (vi tSl Is' tik). 



vitamin (vlf a min). In certain foods a substance which plays a vital role in assimila- 

 tion. 



vitreous (vlt' rg us). Glassy. 



viviparity (viv I par' I tl). The condition which makes possible the producing of 

 living young; adj., viviparous (vl vIp' a rus). 



volant (vo' lant). Capable of flying. 



Von Baer (fon bar') Karl E. Russian naturalist; 1792-1876. 



Von Mohl (f6n mol'), Hugo. German botanist; 1805-1872. 



Wallace, Alfred R. English naturalist; 1823-1913. 



wandering cell. A leucocyte moving about in the tissues of the body. 



Weismann (vis' man), August. German biologist; 1834r-1914. 



Wilson, Henry V. American zoologist, at University of North Carolina; 1863-1939. 



Wolff (volf), Caspar F. German naturalist; 1733-1794. 



Woodruff, Lorande L. American zoologist, at Yale University; 1879- . 



X-chromosome. A chromosome occurring single or paired, the presence of which 

 apparently determines sex. 



Y-chromosome. An unpaired chromosome present in the cells of certain animals and 



also associated with sex. 

 Yerkes, Robert M. American psychologist, at Yale University, 1876- . 

 yolk (yok). Nutritive matter stored in an egg cell; included under the term meta- 



plasm. 

 yolk gland. A gland producing yolk. 

 yoLk stalk. The connection of the yolk sac to the embryo in amniotic vertebrates. 



Zoo- (zo' 6). G.; an animal. 



zooid (zo' old). In a colony a small animal which has been produced by asexual 



reproduction, 

 zygo (zig' 6). G.; yoke, pair. 



zygote (zl' got). The united sperm cell and egg cell, 

 zymogen (zi' m6 j6n). A substance which is developed in a gland cell and which may 



be changed to an enzyme. 



