206 ARACHNII>ES. 



ORDER II. 

 TRACHEARI.E. 



The Arachnid cs which compose this order differ from those 

 of the preceding one in their organs of respiration, which 

 consist of radiated or ramified trache2e(l), that only receive 

 air through two stigmata; in the absence of an organ of circu- 

 lation(2); anxl in the number of their eyes, which is but from 



(1) The traclieze are vessels which receive the aerial fluid and distribute it to 

 every part of the interior of the bod}-, and thus remedy the want of circulation. 

 They are of two kinds. Those tiiat are 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 traches 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 tracheae. In several of the Orthoptera, where they are well developed, 

 cartilaginous arches, formed by appendages of the inferior semi-annuli of the abdo- 

 men, give points of attachment to the muscles.which form them. The branchiae 

 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 trac^x: the others he calls arterial 

 trachex. He also. distinguishes two sorts of stigmata: one- kind, or the ordinary 

 stigmata, simple, and consisting of two membranous lips, furnished with trans- 

 verse striae or fibres, and opening merely by contraction; the others, which he 

 calls tremaercs, are formed of one or two (usually two) horny, movable pieces, 

 opening and closing like shutters. De Geer — Dcscript., Gryllus migratorius — 

 compares them to eye-lids. They are peculiar to certain Orthoptera, and their 

 position shows them to be the stigmata of the niesothorax. M. Leon Dufour — 

 Ann. des Sc. Nat., May 1826 — has given excellent figures of these various kinds of 

 stigmata, but without employing the names of the preceding authors. It would 

 appear from his description of the abdominal stigmata, that they have the charac- 

 ters of the tremaeres, while tliose which he afterwards describes as diffei-ent, are 

 the ordinary stigmata. Our own opinion is that these differences are mere simple 

 modifications of the lips. Reaumur, Mem., I, iv, 16, has figured a stigma of this 

 latter kind, where the lips have an internal border, which, from all appearanceSj 

 must be corneous. By supposing them to be almost entirely of this nature, we 

 have the tremaere of M. de Serres. Certain aquatic larvae have a peculiar respi- 

 ratory apparatus, of which we shall speak hereafter. 



(2) The presence of tracheae excludes a complete circulation, that is to say. 



