GLOSSARY 267 



Tunicin. A cellulose-like substance found in the tunics of certain 



Urochorda. 

 Typhlosole. A longitudinal internal fold in the wall of the intestines 



of some invertebrates, e. g., the earthworm. 



Umbo. In the valve of a clam shell, the raised portion which ends 

 in the beak. It is the first part of the shell to be formed. 



Umbrella. The umbrella-shaped major portion of the body of a jelly 

 fish. 



Uriniferous tube. One of the tubes of an excretory organ. 



Uropod. One of the pair of broad, leaflike appendages of the last 



abdominal segment of a crustacean. 



Uterus. A female organ in which young develop. 



f 



Vagina. In invertebrates, the terminal division of the female repro- 

 ductive duct. 

 Vas deferens. The duct which leads away from the testis. 

 Velum. The ledgelike, delicate, muscular membrane extending inward 



from the subumbrellar margin of certain jelly fishes. 

 Ventral. Under surface; belly. 



Ventricle. A division of the heart which forces blood to the body. 

 Ventriculus. In insects, the division of the alimentary canal which 



leads into the stomach. 

 Vestibule. A depression near the mouth in certain Protozoa as in 



Vorticella. 

 Vestigial. An organ which remains undeveloped and has no function; 



rudimentary as applied in anatomy. 

 Viscera (sing., Viscus). Internal organs taken collectively. 

 Visceral mass. Applied to the portion of a mollusc which contains 



stomach, intestine, liver, gonads, etc. 

 Vitellarium. A female reproductive gland which supplies cells to be 



used as food for developing embryos, as in Bdelloura. 

 Vitelline glands. Same as vitellarium. 



Water tube. One of the tubes between the lamellae of a pelecypod 



gill. 

 Whorl. One of the turns of a gastropod shell. 



Yolk mass. A mass of food material for the nourishment of an em- 

 bryo. 



Zoophyte. An animal which is somewhat plantlike in appearance. 

 Zooid. One of the more or less independent individuals which go to 



make up an animal colony as in Obelia and Bugula. Zooids may 



be nutritive, reproductive, defensive, or sensory. 



