GLOSSARY 411 



Vitelline duct (vi teV lin or vit' el lin dukl'). The duct through which the nutritive 



material produced in a vitelline gland is discharged. 

 Vitelline gland {vi teV lin or vit' el lin gland'). An organ producing yolk to be supplied 



to eggs. 



Viviparity (viv' i par' i ti). The condition of being viviparous. 



Viviparous {vi vip' a rus). Producing young from eggs that are retained in the uterus 



of the mother, with the aid of nutrition derived from the mother through a placenta 



and umbihcal cord. 

 Vocal cords (vo' kol kordz'). Membranous folds stretched across the larynx, which 



by their vibrations in forced currents of air cause the voice. 



Volvocales {vol' vo ka' leez). An order of plants including Volvox, Pandorina, Eudorina, 

 etc. 



Volvox {voV voks) . A small spherical organism composed of flagellated green cells 

 embedded in jelly, in a single layer around a liquid interior. Sometimes regarded 

 as an animal, though more properly included among plants. V. aureus {aiv' re us) 

 of small size; V. rousseletii {roo' se let' i i) very large; V. perglobator {per' glo ha' 

 ter) . 



Vorticella {vor' ti seV la). A ciliated protozoon attached to a contractile stalk. 



Vorticellidae {vor' ti .sel' li dee) . A family of cihated Protozoa to which Vorticella, 

 Epistylis, Carchesium and Zoothamnium belong. 



Wallace, Alfred Russel {woV las). EngUsh naturahst, 1823-1913. 



Xanthophyll {zan' thofil). One of two yellow substances associated with chlorophyll. 

 Xenophanes {ze nof a neez). A Greek philosopher who lived about 570-480 b.c. 



Yucca {yiik' ka). A genus of liliaceous plants having long pointed stiff leaves and a 

 panicle of white flowers. 



Zoogeography {zo' oje og' rafi). The branch of zoology treating of the geographical 

 distribution of animals. 



Zooid {zo' Old). One of the members of a hydroid or siphonophore colony. Often, 

 in a restricted sense, a particular kind of individual, as a hydranth. 



Zoology {zo ol' o ji). The science of animals. 



Zoothamnium {zo' o iham' ni um). A genus of colonial ciUated Protozoa, resembling 

 Vorticella. 



Zygapophysis {zi' ga pof i sis). One of four short projections, two in front and two 

 behind, extending from the upper portion of a vertebra. The posterior pair 

 articulate with the anterior pair of the vertebra next behind. 



Zygote {zi' gote). A cell or individual produced by the fusion of two cells or their 

 nuclei in the process of sexual reproduction. 



