314 
ARACHNIDES. 
ated or ramified tracheae *, that only receive air through two stigmata ; 
in the absence of an organ of circulation!; and in the number of 
their eyes, which is but from two to four The want of sufficiently 
general anatomical observations, has prevented the limits of this 
order from being rigorously determined. Some of these Arachnides, 
the Pycnogonides for instance, exhibit no stigmata ; their mode of 
respiration is unknown. 
The Tracheariae are very naturally divided into those which are 
furnished with chelicerae, terminated by two fingers, one of which is 
moveable, or by one that is equally so ; and into those where these 
organs are replaced by simple laminae, or lancets, which with the 
* The trachcEe 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 are tubular or elastic are formed of three membranes, the 
intermediate of which is composed of a cartilaginous elastic filament spirally con- 
torted ; the two others are cellular. The vesicular tracheae consist of but two mem- 
branes 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 Ortlioptera, where they are w'ell developed, cartilaginous arches, 
formed by appendages of the inferior semi-annuli of the abdomen, give points of 
attachment to the muscles which form them. The branchiae are divided into two 
principal trunks wdiich extend longitudinally throughout the body, one on each side, 
receiving air through lateral openings or stigmata, and then throwing off numerous 
hrauches 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 com- 
municating with them. M. Marcel de Serres distinguishes them by the term pulmo- 
nary trachea : the others he calls arterial trachea. He also distinguishes two sorts 
of stigmata : one kind, or the ordinary stigmata, simple, and consisting of two 
membranous lips, furnished with transverse striae or fibres, and opening merely by 
contraction ; the others, which he calls tremaeres, are formed of one or two (usually 
two) horny, moveable pieces, opening and closing like shutters. De Geer — Descript., 
Gryllus migratorius — compares them to eye-lids. They are peculiar to certain 
Orthoptera, and their position shows them to be the stigmata of the mesothorax. 
M. Leon Dufour — Ann. des Sc. Nat., May 1826 — has given excellent figures of 
these various kinds of stigmata, hut without employing the names of the preceding 
authors. It would appear from his description of the abdominal stigmata, that they 
have the characters of the tremaeres, while those which he afterwards 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, has figured a 
stigma of this latter kind, where the lips have an internal border, which, from all 
appearances, must he corneous. By supposing them to be almost entirely of this 
nature, we have the trdmahre of M. de Serres. Certain aquatic larvae have a pecu- 
liar respiratory apparatus, of which we shall speak hereafter. 
•f- The presence of tracheae excludes a complete circulation, that is to say, 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 — Phasmae — and, although they may possibly exist in 
various Arachnides Trachearia;, 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 caeca or vermiform appendages, which seem to have some analogy with the 
hepatic vessels, and that the tracheae ramify over them ad infinitum. 
;J; According to Miiller the Ilyclrachna taiihrala has six eyes: but may this not 
have arisen from an optical illusion or some mistake? 
