802 



T H U J A T I C K. 



eye large and dark, inclosed in a narrow ring of 

 white ; the legs long and slender, and of a pale brown 

 colour. 



Such are brief notices of the principal thrushes of 

 Europe and North America. There are other spe- 

 cies or varieties in both of these parts of the world ; 

 and there are very many in other parts, of which our 

 limits will not allow us to take notice. Viewed as a 

 family, they are indeed one of the most numerous in 

 the whole class ; and, though not gaudy, they are in 

 general handsome birds, pleasant singers, and valuable 

 as food. 



THUJA (Linnaeus). A genus of ornamental ever- 

 green trees, mostly natives of America and the north- 

 eastern parts of Asia. The flowers are monoecious, 

 and the genus belongs to Crudfera. The arbor 

 vitae is a well-known plant, being common in every 

 shrubbery. The hardy species are raised from seeds, 

 and the greenhouse ones from cuttings. 



THUNBERGIA (Linnaeus). A genus of highly 

 ornamental climbing shrubs, mostly natives of the 

 East. The flowers are didynamous, and belong to 

 AcanthacecB. They are almost ever-flowering plants, 

 produce seeds freely, and if not, are easily propagated 

 by cuttings. 



THYMEL^EA. A natural order, containing 

 eleven genera, and above one hundred species. 

 They are shrubs or trees, very rarely herbs, with 

 joint less branches, sometimes spiny, and the bark 

 tenacious. The leaves are alternate, simple, entire, 

 and without stipules. The flowers are regular, and 

 for the most part collected into axillary or terminal 

 spikes or bunches, though sometimes solitary. The 

 perianth is single, tubular, coloured, with a cleft limb, 

 and the lobes imbricate on aestivation ; stamens defi- 

 nite and peregynous, with two-celled anthers opening 

 lengthwise, laterally or centrally ; the germen is free, 

 simple, one-celled and one-seeded. The wood of 

 some of the genera is remarkably soft, and the fibres 

 so tenacious as to be easily separable, appearing like 

 ribbons of fine lace. The fibres of Lagetta and Direct 

 are capable of being made into cordage. The genera 

 comprised in this order are the following, viz. : 

 Direct, Lagetta, Daphne, Gnidia, Lachncea, Pas&erina, 

 Stellera, Dais, Struthiola, Pimelea, and Trophis. 



THYMUS (Linnaeus). A genus of undershrubs, 

 some of which are cultivated as pot and medicinal 

 herbs. The genus belongs to Labiatce, and are 

 universally distributed over the northern hemisphere. 

 The powerful scent of thyme, and the essential oil 

 extracted from it, renders it a useful plant, whether 

 wild or cultivated. 



THYSANOTUS (Dr. R. Brown). A genus of 

 tuberous-rooted herbs, natives of Australia. The 

 flowers are blue, finely fringed, and hexandrous, and 

 belong to the order AsphodelecE. The species, of 

 which there are four already described, grow freely 

 in a mixture of sandy loam and moor-earth, and are 

 increased by division or by seeds. 



THYSANURA (Leach ; THYSAKOURES, La- 

 treille). An order of apterous hexapod insects, be- 

 longing to the class Ametabola of MacLeay, and 

 distinguished by the more or less cylindric form of 

 the body, provided with only six legs, and destitute 

 of wings, which undergo no other change than an 

 increase of 'size, and furnished on the under side ol 

 the body, at the sides or the extremity, with peculiar 

 organs of motion, consisting, in the family Lepismidee, 

 of a double series of moveable appendages like false 



egs, terminated by articulated setae, and in the 

 Podurulce of an elongated appendage furcate at the 

 xtremity, and applied, when at rest, along the under 

 side of the body. These insects are of small size, and 

 very active, the appendages on the under side of the 

 abdomen enabling them to perform long leaps. They 

 are chiefly found in damp situations under stones, 

 moss, &c. They have been much neglected by 

 naturalists ; but a valuable memoir is published in 

 the first volume of the Transactions of the Entomo- 

 ogical Society of London, upon the Irish species, by 

 R. Templeton, accompanied with beautiful figures. 

 Some of the species, however, appear to us to be 

 established upon insects in the larva state. 



These insects are very interesting, not only on 

 account of their position amongst annulose animals 

 (being regarded by Latreille and Leach as true 

 insects, and by MacLeay as belonging to a distinct 

 class, Ametabola], but also from the modifications in the 

 structure of the mouth ; some of the species possess- 

 ing a development of the trophi as great as in the 

 most perfectly mandibulated insects ; whilst in others 

 the mouth is so obscurely organised, that neither 

 Latreille, Savigny, nor Templeton, have been able to 

 trace its formation. In some species the eyes are 

 merely rudimental ocelli, but in others they are per- 

 fectly reticulated. We may also specially notice the 

 beautiful scales with which the body is covered, and 

 the apparent want of spiracles along the sides of the 

 body, and which Latreille, notwithstanding a very 

 minute examination, was unable to discover. M. 

 Guerin has, however, very recently presented to the 

 French Academic des Sciences a memoir, in which 

 he announces the existence of bronchias in one of the 

 species of this order. They are placed under the 

 abdominal segments, and by the side of those ap- 

 pendages which are compared to the false legs of the 

 Crustacea. They are inclosed in little membranous 

 bags of a similar organisation to those of the respi- 

 ratory organs of a great number of the inferior 

 Crustacea. This discovery of bronchiae in these 

 insects appears important in various respects, and 

 more especially because it establishes a link between 

 two classes hitherto regarded as certainly separate 

 as regards their mode of respiration. 



TICK. The species of insects of which the genus 

 Ixodes is composed are thus named. They are of 

 small size, and belong to the class Arachnida, and 

 order Monomerosomata or Acari. The body is swollen 

 and leathery, having on the upper side, in front, a 

 scaly plate. The head is small, and furnished with a 

 powerful rostrum composed of two retroserrated 

 plates, which the insect inserts into the flesh of dogs 

 and other animals upon which it is parasitic, and 

 upon whose blood it subsists. The palpi are articu- 

 lated, and enclose the sucker. In the West Indies 

 (hey attack the horse and ass in such quantities, that 

 it is the usual practice to have these animals fetched 

 up from grass once a-week to be " ticked." They 

 especially attach themselves at the base of the ear, 

 and, if neglected, will sometimes become so numerous 

 that the animal loses all power of raising its ears at 

 will. Their powers of reproduction are so great that 

 the animals attacked sometimes sink under their 

 attacks. 



The typical species is the Ixodes ricinus (Acarus 

 ricinus, Linnaeus), which is parasitic on the dog. It 

 is serviceable to anoint the infested parts with oil or 

 soft soap. The species of this genus require a more 



