GLOSSARY 177 



variation. A modification, alteration, or deviation from the 



typical or usual condition, 

 vein. A vessel which carries blood to the heart; one of the 



ribs in the wings of insects. 

 velum. A circular membrane that partly incloses the space 



beneath the umbrella in medusae. 

 ventral. At or toward the under or belly surface, 

 viscera. The internal organs taken as a whole. 



yeast. A unicellular, colorless plant which causes an alco- 

 holic fermentation of carbohydrates. 



zob'id. One of the single individuals in a colony of animals, 

 zobspore. A spore provided with one or more flagella by 



which it swims in the water, 

 zygospore. A spore formed by the union of two zoospores, 



or by union of protoplasm from two plants. 



