GLOSSARY 



509 



Swim -bladder, or Air-bladder, a g-as-contain- 

 ing- outgrowth from the digestive tube of 

 some Fishes, which serves as a hydrostatic 

 orgfan. 



Symbiosis (Gk. ^_>//i, together; bidsis,\i{e). See 

 Mutualism, 



Symmetry (the Greek name), regularity of build. 

 In Radial Synimctry the parts of the body are 

 arranged with reference to a centre of sym- 

 metry, e.g. in a coral polype. In Bilateral 

 Symmetr}', as seen, e.g.^ in a Fish, we can 

 distingfuish right and left sides, anterior and 

 posterior ends, upper and lower surfaces. 



Sympathetic nervous system, a part of the 

 nervous system concerned with the reg^ula- 

 tion of the blood-vessels and internal org-ans. 



Syndactylous (Gk. syn, together; daktyWs, a 

 finger or toe), with some of the dig-its bound 

 closely tog'ether. 



Syrinx (Gk. for reed-pipe), the vocal org^an or 

 voice-box of a Bird, situated where the wind- 

 pipe divides into a branch [brojichus) for each 

 lung". 



Systemic, applied to a heart which contains 

 pure blood only. 



Tail-coverts, feathers covering" the tail-quills. 



Tarsale, pi. -ia, one of the distal elements of 

 the tarsus. 



Tarso-metatarsus, a bone in the leg of a Bird, 

 formed by the fusion of part of the ankle- 

 skeleton (tarsus) with three of the instep- 

 bones (metatarsus). 



Tarsus (Gk. fars(js, the broadest part of the 

 foot): (i) in Vertebrates, the skeleton of the 

 ankle; (2) in Insects, the foot. 



Teeth : (i) in Vertebrates, hard structures used 

 for securing" prey, or for breaking up food ; 

 ( ) hard projections with which the radula 

 (which see) of Molluscs is studded; (3) small 

 projections usually present in the " hing^e " 

 of a bivalve shell : they fit into correspond- 

 ing- sockets, and prevent shifting- when the 

 shell opens or closes. 



Telson (Gk. for a termination), in higher 

 Crustaceans, the last seg^ment of the abdo- 

 men. It bears no limbs, and is the middle 

 part of the tail-fin. 



Tendon, a fibrous inelastic band by which a 

 muscle is attached to a part of a skeleton. 



Tensor muscles (L. /ejido, tentinn^ tensum, to 

 stretch), in Birds, muscles which keep the 

 wing-membranes on the stretch. 



Tentacle (L. tento^ I feel), a soft feeler, e.g. 

 one of the " horns " of a Snail, or one of the 

 numerous fieshy filaments surrounding the 

 mouth-end of a Sea-Anemone. 



Tentaculocyst (tentacle; Gk. cystis^ a bladder), 

 in some Jelly-Fishes, a short specialized ten- 

 tacle servings as a balancing- org:an. 



Tergum, pi. -a (L. for the back), in Arthro- 

 pods, that part of the exoskeleton covering" 

 the dorsal surface of a seg-ment. 



Test (L. testa^ a shell), the firm investment of 

 Ascidians, Echinoderms, and some other 

 lower animals. 



Tetradactyle(Gk./^//'a, four; daktylos, a finger 



or toe), possessing four digits. 

 Thoracic duct, a narrow tube lying imme- 

 diately ventral to the backbone. It receives 

 most of the lymphatics, and opens into the 

 great veins at the base of the neck. 



Thread-cell. See Nettlhig-cell. 



Thymus gland (Gk. ihy)iios^ the heart), a 

 fatty -looking" ductless gland situated (in 

 Mammals) near the base of the heart. 



Thyroid gland (Gk. thyreos, a shield; eidfis^ 

 resemblance), a ductless gland in the neck- 

 region, having something" to do with reg"u- 

 lating" the nutrition of the body. 



Tibia (the Latin name for(i)) : (i) the shin-bone 

 of Vertebrates ; (2) that region of the leg" in 

 Insects, &.C., which adjoins the foot. 



Tibiale, in the tarsus, a proximal element situ- 

 ated on the side next the great toe. 



Tibio-tarsus, in Birds, a bone formed by fusion 

 of the shin-bone (tibia) with part of the ankle- 

 skeleton (tarsus). 



Tissue, an ag-g-regate of cells specialized for 

 the performance of some particular kind of 

 physiological work. 



Tornaria, pi. -se (Gk. tornod^ I make round), 

 the ciliated larva of some species of acorn- 

 headed worm. 



Tortoise-shell, an ornamental product pre- 

 pared from the horny epidermic plates of 

 certain Turtles. 



Trachea (Gk. tracheliaius, relating- to the 

 neck), the wind-pipe. 



Tracheae. See Tracheal iiibes. 



Tracheal gill, In some aquatic Insects, a gfill 

 traversed by air-tubes [trachece). 



Tracheal tubes, the air-tubes of air-breathing- 

 Arthropods. 



Tragus, a pointed projection (" earlet ") within 

 the ear of a true Bat. 



Trepang, dried Sea-Cucumbers, an important 

 article of food in the Far East. 



Trez-tine. See Antler-royal. 



Trichinosis, a disease due to the attacks of 

 minute thread-worms (Trichinae). 



Trichocysts (Gk. tlirix^ trichos, a hair ; cystzs, 

 a bladder), in some Animalcules, micro- 

 scopic rods discharged from the outer layer 

 of the body as a means of defence, and pro- 

 bably of Irritant nature. 



Tridactyle (Gk. trl, three; daktylos, a fing-er 

 or toe), possessing three dlg"lts. 



Triploblastic (Gk. trlploos, threefold; blastos, 

 a bud), applied to animals in which the body 

 essentially consists of three cellular layers. 



Trochanter (Gk. for a process of the thig^h- 

 bone), in Insects, the small second joint of 

 the leg. 



Trochosphere (Gk. trochus, a wheel; sphaira, 

 a sphere), in various Invertebrates, a bilateral 

 ovoid larva, with a well-marked head-lobe, at 

 the base of which is a circlet of large cilia. 



Tubercle, a rounded projection, e.g. on the 

 crown of a tooth. 



