TOURMALINE. 



[ 775 ] 



TRACHELINA. 



Achorion. Mycelium somewhat ramose, 

 articulated, joints terminating in round, oval, 

 or irregular spores (conidia ?). 



Speira. Spores connate into concentric 

 filaments, forming lamina? resembling a 

 horseshoe, finally separating, 



Trimmatodroma, Spores more or less 

 curved, multiseptate, chained in beaded 

 rows, finally separating. 



Gyrocerus. Spores connate into spirally 

 coiled filaments, finally separating. 



Dictyotponum. Spores tongue-shaped, re- 

 ticularly cellular (fig. 172, p. 260). 



TOURMALINE. Sections of the crys- 

 tals of this mineral, cut parallel to the axis, 

 were formerly used as polarizers or ana- 

 lyzers. They are now usually replaced by 

 Nicol's prisms (INTRODUCTION, p. xx). 

 Crystals of the quinine-salt (QUININE) form 

 cheap substitutes for either. The crystals of 

 tourmaline belong to the rhombohedric 

 system. They consist principally of silica 

 with alumina, containing also boracic acid, 

 magnesia, iron, &c. j but their composition 

 is not constant. 



Good tourmalines are transparent, brown- 

 ish or pinkish j the colourless ones do not 

 polarize. 



BIBL. Pereira, Polarized Light', Nau- 

 mann, Mineralogie, 319. 



TOUS-LES-MOIS. A kind of fecula 

 consisting of the starch of species of Canna, 

 remarkable for the large size, great transpa- 

 rency, and numerous striae of the granules 

 (PI. 46. fief. 25). The mixture of any of the 

 common kinds of starch with Tous-les-mois 

 is readily detected by microscopic exami- 

 nation. The granules are excellent sub- 

 jects for studying the physical characters of 

 starch, in particular the appearance with 

 polarized light (PI. 39. fig. 40), &c. See 

 STARCH. 



TOXOXIDEA, Donkin. A proposed new 

 genus of Diatomaceae, the frustules of which 

 resemble those of Pleurosiyma, except that 

 the longitudinal line is curved on each side 

 of the median nodule in the same direction, 

 so as to resemble a bow. Two species. 



T. Grer/oriana (PI. 51. fig. 24). 

 BIBL. Donkin, Micr. Jn. 1858, vi. 12 ; 

 Rabenht. Alg. i. 243. 



TRACHE'A. See LUNGS. 

 TRACHE'^E OF INSECTS, &c The re- 

 spiratory tubes of Insects and Arachnida. 



Trachea (PI. 34. fig. 17 ; PL 85. fig. 2 h] 

 are cylindrical tubes containing air. They 

 are broadest at their origin from the spira- 



cles, afterwards branching freely, the minute 

 branches being distributed to all parts of the 

 body and anastomosing freely. By reflected 

 light they appear white, with a metallic 

 lustre, or slightly iridescent ; by transmitted 

 light the smaller ones are black, the larger 

 usually of a violet tint. 



The tracheae consist of two coats, between 

 which lies a spiral fibre (PI. 34. fig. 17) ; in 

 the larger trunks a second external envelope 

 exists. The fibre becomes more slender and 

 indistinct in the smaller trachea! branches, 

 until it finally disappears. The outer mem- 

 brane appears to arise from the confluence 

 of cells ; for in the tracheae of caterpillars 

 and other larvae of insects, the remaining 

 nuclei are visible (PL 34. fig. 17). The 

 inner coat forms a pavement epithelium. 

 The spiral fibre arises from the splitting up 

 of a homogeneous membrane deposited in 

 the space bounded by the confluent cells of 

 the outer membrane. 



In many insects the tracheae are furnished 

 with dilatations forming air-sacs, in which 

 the spiral fibre is absent. 



When larvae are fed with indigo or car- 

 mine, or when the dorsal vessel is injected 

 with colouring-matter, the tracheae become 

 coloured, which some authors believe to 

 arise from the nutritive liquid circulating 

 between the membranes of the tracheae ; 

 whilst by others this circulation, or the ex- 

 istence of a space between the tracheal 

 membranes, is denied. 



BIBL. That of INSECTS ; Newport, Phil. 

 Tr. 1836, 529; Platner, Mullens Archiv, 

 1844, xxxviii.; Stein, VergL Anat. Insek- 

 ten ; Agassiz, Ann. Sc. Nat. 3. xv. ; Bassy, 

 ibid. ; Joly. ibid. xii. ; Blanchard, Compt. 

 Rend. 1851 ; Ann. N. H. 1852, ix. 74; Du- 

 four, Compt. Rend. 1851, Ann. N. H. 1852, 

 ix. 435 ; Meyer, Siebold $ Kolliker's Zeitschr. 

 i. 175 ; Moseley, P)>oc. Roy. Soc. No. 153. 

 vol. xxii. 344, 1874 ; Gerstacker, Siebold fy 

 Kolliker's Zeitschr. ii. 204, 1874; Landois, 

 Zeit. iviss. Zool. xvii. 



TRACHEAE OF PLANTS. This name 

 was formerly applied to the unreliable 

 SPIRAL Vessels of Plants, from their resem- 

 blance to the tracheae of Insects. 



TRACHELI'NA. A family of Holo- 

 trichous Infusoria. 



Char. Body without regular spiral teeth 

 or foot ; parenchyma excessively contrac- 

 tile ; mouth and oesophagus very dilatable. 



BIBL. Clap. & Lachm. Inf. p. 291. 



