GLOSSARY. 



TRACHEARIA. The division of Arachnida which breathe by means of 



tracheae. 



TREMATODA (Gr. trema, a pore). An order of Scolecida. 

 TRICHOCYSTS (G-r. tkrix, hair ; and kustis, a cyst). Peculiar cells found in 



certain Infusoria, and very nearly identical with the ' thread-cells ' of 



Coelenterata. 



TRILOBITA (Gr. treis, three ; and lobos, a lobe). An extinct order of Crus- 

 taceans. 

 TRITOZOOIDS (Gr. tritos, third; zobn, animal; and eidos, form). The zooid 



produced by a deuterozooid ; that is to say, a zooid of the third generation. 

 TROCHAL (Gr. trochos, a wheel). Wheel-shaped ; applied to the ciliated disc 



of the Rotifera. 

 TROCHOID (Gr. trochos, a wheel, and eidos, form). Conical with a flat base; 



applied to the shells of Foraminifera and Univalve Molluscs. 

 TROPHI (Gr. trophos, a nourisher). The parts of the mouth in insects, 



which are concerned in the acquisition and preparation of food. Often 



called ' instrumenta cibaria.' 

 TROPHOSOME (Gr. trtpho, I nourish; and soma, body). Applied collectively 



to the assemblage of the nutritive zooids of any Hydrozoon. 

 TRUNCATED (Lat. trunco, I shorten). Abruptly cut off; applied to univalve 



shells the apex of which breaks off, so that the shell becomes 'decollated ' 

 TUBICOLA (Lat. tuba, a tube ; and coh, I inhabit). The order of Annelida, 



which construct a tubular case in which they protect themselves. 

 TTJBICOLOUS. Inhabiting a tube. 



TUKICATA (Lat. tunica, a cloak). A class of Molluscoida which are enve- 

 loped in a tough leathery case or ' test.' 

 TURBELLARIA (Lat. turbo, I disturb). An order of Scolecida. 

 TURBINATED (Lat. turbo, a top). Top-shaped, conical with a round base. 



UMBELLATE (Lat. umbella, a parasol). Forming-an umbel ; i.e. a number of 



nearly equal radii all proceeding from one point. 

 UMBILICUS (Lat. for navel). The aperture seen at the base of the axis 



of certain univalve shells, which are then said to be 'perforated* or 'um- 



bilicated.' 



UMBO (Lat. umbo, the boss of a shield). The beak of a bivalve shell. . 

 UMBRELLA. The contractile disc of one of the Lucernarida. 

 UNCINATE (Lat. uncinus, a hook). Provided with hooks or bent spines. 

 UNILOCULAR (Lat. units, one ; and loculus, a little purse). Possessing a single 



cavity or chamber. Applied to the shells of Foraminifera and Mollusca. 

 UNIVALVE (Lat. unus, one; valvce, folding-doors). A shell composed of a 



single piece or valve. 

 URTICATING CELLS (Lat. urtica, a nettle). (See Cnidse.) 



VACUOLES (Lat. vacuus, empty). The little cavities formed in the interior 

 of many of the Protozoa by the presence of little particles of food, 

 usually surrounded by a little water. These are properly called ' food- 

 vacuoles,' and were supposed to be stomachs by Ehrenberg. Also the 

 clear spaces which are often seen in the tissues of many C&lenterata. 



VARICES (Lat. varix, a dilated vein). The ridges or spinose lines, which 

 mark the former position of the mouth in certain univalve shells. 



VASCULAR (Lat. vas, a vessel). Connected with the circulatory system. 



VELUM (Lat. a sail). The membrane which surrounds and partially closes 

 the mouth of the ' disc ' of Medusa, or medusiform gonophores. 



VENTRAL (Lat. venter, the stomach). Relating to the inferior surface of the 

 body. 



