512 APPENDIX 



Turgor. Pressure within a cell, largely due to the absorption of water, 



which distends or holds rigid the cell wall. 

 Typhlosole. A median dorsal invagination along the entire length of 



the intestine of the Earthworm which increases the area of the digestive 



and absorptive surface. 



Umbilical Cord. A Mammalian structure, commonly known as the 

 navel cord, by which the embryo is attached to the placenta. The blood 

 vessels from the embryo to the placenta pass through it. See Placenta. 



Unguiculate. Provided with claws. 



Uniformitarian Doctrine. An interpretation of the present condition of 

 the Earth on the assumption of similarity of factors at work during 

 past ages and to-day. 



Uniparental. Derived from a single progenitor; e.g., in asexual reproduc- 

 tion. See Biparental. 



Urea. Nitrogenous waste product of animal metabolism. Formed as such 

 in the liver, removed from the blood by the kidneys and eliminated from 

 the body chiefly in urine. CO(NH 2 )2- A major part of the nitrogen is 

 excreted in this form in human urine. See Creatinine and Uric Acid. 



Ureter. A tube carrying urine from kidney to the cloaca or to the urinary 

 bladder. 



Uric Acid. A nitrogenous waste product. Present in small quantity in 

 the urine of Man. 



Urogenital. Relating to the urinary and reproductive systems. 



Urostyle. Terminal rod-like bone of the vertebral column of the Frog. 



Uterus. Lower portion of the oviduct (or oviducts) modified for the 

 retention of the eggs, temporarily or during development. 



Uterus Masculinus. Remnant of the pronephric ducts in some male 

 Mammals. 



Utriculus. The posterior sac of the labyrinth of the ear into which the 

 semicircular canals open. 



Vagina. Passage leading from the uterus to the exterior. 



Vasomotor Nerves. Nerves which regulate the caliber of small arteries 

 by bringing about relaxation or contraction of the muscular layer of 

 their walls. 



Vermiform Appendix. Blind outpocketing of the large intestine near its 

 origin from the small intestine. Vestigial end of the caecum. Found 

 only in Apes and Man. 



Vertebra. One of the series of elements forming the backbone, or ver- 

 tebral column. 



Vertebrate. An animal with a backbone, or vertebral column. See 

 Chordate. 



