V AG 



VAL 



part of the excrement of birds ; and vast 

 accumulations of that urate exist in the 

 •guano, or decomposed excrement of 

 aquatic birds, by which many of the 

 small islands on the Coast of Peru and 

 Chili are covered, and which is used as a 

 manure. 



URILE. A compound radical, sup- 

 posed to exist in uric acid and the pro- 

 ducts of its decomposition. It is a com- 

 pound of 2 atoms of cyanogen and 4 

 atoms of carbonic oxide. 



URN. The peculiar theca or capsule 

 of mosses, containing the spores. It 

 is placed at the apex of a stalk or 

 seta, bearing on its summit a hood or 

 calyptra, and closed by a lid or opercu- 

 lum. 



URODELA. An order of Amphibious 

 animals, including the Salamanders, 

 Water-newts, &c., in which the gills dis- 

 appear in the perfect state, but the tail is 

 retained. They may be distinguished 

 into the Tritons, which, like the frogs, 

 exhibit aquatic habits even in the adult 

 state ; and the true Salamanders, which 

 are more analogous to the toads in their 

 appearance and habits. I 



URSA MAJOR. The Great Bear; a 

 northern constellation, consisting of 87 | 



stars, the principal of which is named 

 Dubhe. 



Ursa Minor. The Lesser Bear ; a 

 northern constellation, consisting of 24 

 stars, the principal of which is the Pole 

 Star. 



UR'SID^ (ursus, a bear). The Bear 

 tribe of carnivorous vertebrate ani- 

 mals. These are the true plantigrade 

 carnivora. Most of them possess several 

 tuberculous teeth. 



URTICA'CEiE (urtica, a nettle). The 

 Nettle tribe of Dicotyledonous plants. 

 Trees or shrubs with leaves alternate; 

 flowers apetalous, solitary, or clustered ; 

 ovarium superior 2-celled ; fruit, a simple 

 indehiscent nut. 



UTRICLE (utriculus, dim. of uter, a 

 leathern bag). Cystidium. In Botany, 

 a simple fruit, 1-celled, one or few- 

 seeded, superior, membranous, fre- 

 quently dehiscent by a transverse in- 

 cision. It may be described as a cary- 

 opsis, the pericarp of which has no adhe- 

 sion with the integuments of the seeds. 

 It differs from the pyxidium in texture, 

 being strictly simple, that is, not pro- 

 ceeding from an ovarium with obliterated 

 dissepiments. It occurs in the ama- 

 ranth, in chenopodium, &c. 



VA'CUUM {vacuus, empty). Literally, 

 an empty place, or space void of matter. 

 This term generally denotes the space 

 enclosed by a vessel from which the 

 atmospheric air and every other gas has 

 been excluded, as in the Torricellian 

 vacuum above the surface of the mer- 

 cury in the barometer tube, and the Gue- 

 rickian or Bnylean vacuum of the air- 

 pump. The latter vacuum is always im- 

 perfect ; the vessel is, nevertheless, 

 called an exhausted receiver. 



VAGA'NTES {vagor, to wander). A 

 tribe of spiders comprising those which 

 watch their prey from the web, and also 

 frequently run with agility in pursuit 

 of their prey. 



VAGATRI'CES {vagor, to wander). 

 Wanderers ; an order of birds, which, 

 being equally well adapted for walking 

 and for flying, might be designated ter- 

 restrial. They walk with ease, leap under 

 excitement, or even run with consider- 

 able speed. They include the corvine and 

 the graculine bir** 

 355 



VAGI'NA. Literally, a sheath; and 

 hence applied, in Botany, to a leafy ex- 

 pansion surrounding the stem of some 

 monocotyledonous plants ; occasionally 

 the petiole embraces the branch from 

 which it springs, and in such case is 

 said to be sheathing, and is even called a 

 sheath, or vagina, as in grasses. 



VA'GINATED {vagina, a sheath). A 

 designation of those polyps which are en- 

 closed in a calcareous sheath or tube, 

 and are also called tubiporidcB. 



VALERIANA'CEiE. The Valerian 

 tribe of Dicotyledonous plants. Herbs 

 with leaves opposite ; flowers corymbose, 

 panicled, or in heads ; stamens distinct ; 

 ovarium inferior 2-celled ; fruit dry, 

 indehiscent. 



VALERIANIC ACID. Valeric acid. 

 An acid obtained by distillation of the 

 root of the Valeriana officinalis with water, 

 as long as it reddens litmus. Its salts 

 are called valerianates and valerates. 



VALLEY {vallis). A space lying be- 

 tween opposite ridges of mountains or of 



