476 GLQSSARY. 



TUBULIBRANCHIA'TA, an order of mollusks, to which the Verme- 

 tus belongs. The gills in some of the species are arranged 

 in a somewhat tubular form, and follow all the windings of 

 the convoluted shell. 



TUNICA'TA, a class of molluscous animals, having a leathery 

 or a membranous covering, instead of one formed of shelly 

 matter. In many other respects their structure is very re- 

 markable and peculiar. Lat. tunica, a tunic. 

 TYPICAL, that which is regarded as the type or representative 



of a particular group. 

 UNDULATION, a movement in curved or arching lines resembling 



that of a wave. Lat. undulatus, from unda, a wave. 

 UNIQUE, singular, single, one only. French, unique. 

 UNIVALVE, a term applied to a shell which, like that of the 



whelk or the limpet, consists of only one piece. 

 VACUUM, a space unoccupied by matter most usually employed 



to denote a space from which the air has been exhausted. 

 VENTRAL, belonging to the belly. Lat. venter, ventris, the belly. 

 VENTRICLE, a term applied to one or to two of the cavities in 



the heart of the vertebrate animals. 

 VERMIFORM, worm-shaped. Lat. vermis, a worm. 

 VERMIGRADE, moving like a worm. Lat. vermis, a worm, and 



gradior, I advance. 



VERTEBRAL COLUMN. " Vertebral, as consisting of segments of 



the skeleton which turn one upon the other, and as being 



the centre on which the whole body can bend and rotate; 



from the Latin, verto, vertere, to turn." OWEN. 



VESICLE, a small enclosed space like a little bladder. Lat. 



vesicula. 

 VIBRATILE, possessing the power to vibrate. Lat. vibrare, to 



shake. 



VITALISED, with the power of sustaining life. ^ The term is ap- 

 plied to water containing atmospheric .air, and which is 

 thereby fitted for the respiration of aquatic animals. Lat. 

 vita, life. 

 VIVIFIED, endued with life. Lat. vivere, to live vivificare, to 



cause or give life. 

 VIVIPAROUS, producing the young alive. The \vord is used in 



opposition to oviparous, already mentioned. 

 WEALDEN FORMATION, a geological term applied to a fresh- 

 water deposit in the South of England. It belongs to the 

 upper part of the secondary series of rocks, and attests the 

 former existence in that region of a large river. 

 ZOOLOGY, that department of science that treats of the struc- 

 ture, habits, and classification of animals. Gr. zoon, an 

 animal, and logos, a discourse. 



ZOOLOGIST, one who has acquired a knowledge of Zoology. 

 ZOOPHYTES, a class of radiated animals, formerly supposed to 

 partake of the nature of both animals and plants. Gr. zoon 

 an animal, and phyton, a plant. 



