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Show 206 A HACUNIDES. ORDER II. TRACHEARLE. The Arachnides which compose this order differ from those of the preceding one in their organs of res pi ration, which consist of radiated or ramified trachere(l ), that only receive air through two stigmata; in the absence of an organ of circu. lation(2); and in the number of their eyes, which is but from (1) The tracbe~ are vessels which receive the aerial fluid and distribute it to every part of the interior of the body, and thus remedy the want of circulation. They are of two kinds. Those that nre tubular or elastic are formed of three membranes, the intermediate of which is composed of a cartilaginous elastic fila· ment spirally contorted; the two others are cellular. The vesicular trachea: consist of but two membranes of the latter description. They are a kind of pneumatic pouches susceptible of being inflated and depressed. Aquatic Insects, and others that are aerial, are deprived of them. They communicate with each other by tubular trachea:. In several of the Orthoptera, where they are well develope~ cartilaginous arches, formed by appendages of the inferior semi-annuli of the abdomen, give points of attachment to the muscles which form them. The brnnchiz are divided into two principal trunks which extend longitudinally throughout the body, one on each side, receiving air through lateral openings or stigmata, and then throwing off numerous branches and twigs which distribute it. In several Insects, however, there are two other trunks more or less long, situated between the two preceding ones and communicating with them. M. Marcel de Serres distinguishes them by the term pulmonary tracltew: the others he calls arterial tracltew. lie also distinguishes two sorts of stigmata: one kind, or the ordinary stigmata, simple, and consisting of two membranous lips, furnished with tral\5· verse sh·ire or fibres, and opening merely by contraction; the others, which lle calls trhnaeres, are formed of one or two (usually two) horny, movable pieces, opening and closing like shutters. De Geer-JJescript., Gryllus migratoriuscompnres them to eye-lids. They are peculiar to certain Orthoptera, and their position shows them to be the stigmata of the mesothorax. M. Leon DufourAnn. des Sc. Nat., May 1826-has given excellent figm·es of these various kinds of stigmata, but without employing the names of the preceding authors. It would appear from his desct·iption of the abdominal stigmata, that they have the charac· ters of the tremacrcs, while those which he aftcrwarrls describes as different, are the ordinary stigmata. Our own opinion is that these differences are mere simple modifications of the lips. Reaumur, Mem., I, iv, 16, bas figured a stigmn of this btter kind, where the lips have an internal bordet·, which, from all appenran~es, must be corneous. By supposing them to be nlmost entirely of this nature, we have the tt·emac!re of M. de Serres. Cc;rtain aquatic larva: have a peculiar respi· ratory apparatus, of which we shall speak hereafter. (2) The presence of trachea: excludes a complete circulation, that is to say, TRACIIEARllE. 207 t four( I)· The want of sufficiently general anatomical ~~:er~ations, has prevented the limits of this order from b • rigorously determined. Some of these Arachnides, the Peymcgn ogonides for instance, ex h1'b 1' t no sti.g mata; t h e1. r mo d e of respiration is unknown. . . . . The Trachearire are very naturally d1v1ded mto those wh1ch re furnished with chelicerro, terminated by two fingers, \e of which is movable, or by one that is equally so; and ~nto those where these organs are replaced by simple laminm, or lancets, which with the ligula constitute a sucker. Most ofthcse animals, however, being vet·y small, great difficulties necessarily accompany these investigations, and it is readily perceived that such characters should only be resorted to when it is impossible to avoid it. . FAMILY I. PSEUDO-SCORPIONES. In this family we find the thorax articulated, its first segment much the largest, and resembling a corselet; the abdomen is very distinct and annulated, and the pal pi vet·y large and in the form of legs or claws. There are eight legs in each sex, with two equal hooks at the extremity of the tarsi, the two anterior ones, at most, excepted, and two apparent chelicerre terminated by two fingers and two toes, formed by the first joint of the pal pi. They are all terrestrial, and have an oval or oblong body. This family comprehends but two genera. the distribution of the blood to the different parts of the body, and its return from the organs of respiration to the heart. Thus, although some vessels have recently been discovered in certain Insects-Phasmre-and, although they may possibly exist in various Arachnides Tracheari.-e, it does not exclude them from the general system. M. M. de Serres has observed that the intestinal tube of the Phalangium gives off numerous creca or vermiform appendages, which seem to have some a~alogy with the hepatic vessels, and that the trache.-e ramify over them ad infi· nttum. 0) According to MUller the llydraclma umbmta has six eyes: but may thia not have arisen from an optical illusion or some mistake> |