vacuole (vak'you-ohl) : drop of liquid in the cyto- 

 plasm of plant cells particularly; contractile 

 vacuole: special vacuole in protozoa used in 

 excretion of liquid wastes; food vacuole: also 

 in protozoa, particle of food surrounded by 

 water within the cell. 



vagina (va-jeye'na) : in mammals the passage 

 from the uterus to the outside of the body 

 through which the embryo passes at birth. 



variety (var-eye'e-tee) : subdivision within a spe- 

 cies based on some hereditary difference con- 

 sidered too small to make a new species. 



vascular (vas'cue-lar) bundle: a group of con- 

 ducting tubes and wood cells in a young dicot 

 stem and root and leaf or in a monocot stem. 

 In older stems they are replaced by the vas- 

 cular cylinder. 



vascular (vas'cue-lar) cylinder: the cylinder in or 

 near the center of a dicot root and stem, 

 holding the water-conducting tubes. 



vegetative propagation (vej'a-tay'tiv prop-a-gay'- 

 shun) or reproduction: asexual reproduction 

 in higher plants from parts other than the 

 reproductive organs, such as roots. 



vein (vain) : vessel that carries blood toward the 

 heart. In a leaf the vein consists of conduct- 

 ing tissues and wood fibers. 



venereal (ven-ee'ree-al) disease: disease spread 

 commonly through the sex organs, such as 

 syphilis and gonorrhea. 



ventral: under or belly side of an animal; oppo- 

 site of dorsal. 



ventricle (ven'tri-k'l) : in the vertebrate Heart the 

 chamber (in higher vertebrates there are two 

 ventricles) which pumps blood into the ar- 

 tery or arteries. 



vertebra (ver'te-bra) : one of the bones compos- 

 ing the backbone of vertebrates. 



vertebrates (ver'te-brayts) : animals with back- 

 bones, making up a subphyhmi of the chor- 

 date phylum. 



vestigial ( ves-tij'ee-alj structures: in animals or 

 plants imperfectly developed structures hav- 

 ing little or no use, but which were useful 

 in preceding organisms. 



villus (vill'us) : one of the many tiny projections 

 of the lining of the small intestine into which 

 digested foods are absorbed. 



virus (vy'rus), or filterable virus: ultramicro- 

 scopic agents of infection, requiring living 

 cells for multiplication; small enough to pass 

 through a porcelain filter. 



vitamin (vye'te-min) : one of a group of sub- 

 stances in foods occurring in small amounts 

 and necessary to keep the body in a healthy 

 condition. 



warm-blooded: applied to animals whose body 

 temperature remains relatively constant. 



weathering: breaking up of rocks or changes 

 in their composition caused by the action of 

 the atmosphere. 



weed: a plant "out of place," that is, a plant grow- 

 ing where it is not wanted. 



xylem ( zye'lem ) : woody inner portion of the vas- 

 cular cylinder in root and stem of ferns and 

 seed plants. 



yolk: that part of the egg of some animals, such 

 as the fish, frog, bird, and others, which sup- 

 plies food to the developing embryo. 



zoologist (zoh-ol'o-jist: person who makes a spe- 

 cial study of animals. 



zygospore (zeye'go-spore) : cell with a thick cell 

 wall formed by the fusion of two similar 

 gametes in plants. 



zygote (zeye'goati: fertilized egg cell in plants 

 and animals. 



598 



