B84 THE ARACHNOIDAE. $$ 311, 312. 
CHAPTER VII. 
RESPIRATORY SYSTEM. 
§ 311. 
The higher Arachnoidae respire by tracheae, or by lungs; but in the 
lower, namely, the Tardigrada,® the Pycnogonidae,® and some parasitic 
Acarina,® no traces of respiratory organs have yet been found. With 
these animals therefore the respiration must be cutaneous. 
Many Acarina, the Opilionina, the Pseudoscorpii and the Solpugidae, 
breathe by tracheae, while the Araneae, the Phrynidae and the Scorpio- 
nidae breathe by lungs. On this account, these animals have been divided, 
in zoological systems, into the Arachnidae tracheariae and pulmonariae. 
But this classification is valueless, since it has been shown that the Araneae 
possess both lungs and tracheae. 
§ 312. 
With the Acarina, the Tracheae are exceedingly tenuous, and it is only im 
the larger species that the spiral filament of these organs can be observed. 
They arise usually by a simple tuft from two stigmata which are sometimes 
concealed between the anterior feet, as with the Hydrachnea, the Oribatea, 
and the Trombidina, sometimes very apparent above the third pair of legs, 
as with the Gamasea, and sometimes behind the last pair of legs, as with 
the Ixodea.© 
With the Hydrachnea, which live in the water and never come to the 
surface to take in air, the tracheae possess, probably, the power to extract. 
from the water the air necessary for respiration.® 
With the Pseudoscorpii, there is, on the ventral surface of the two first 
abdominal segments, a pair of lateral stigmata, with four short but large 
trachean trunks from which arise numerous unbranched tracheae spread- 
ing through the entire body. 
1 See Doyere, loc. cit. p. 316. 
2 See Quatrefages, loc. cit. p. 76. 
3 Demodex, Sarcoptes, Acarus, &c. 
1 With Trombidium, there arise two simple 
and very distinct trachean tufts from the two 
stigmata situated behind the second pair of legs 
(Treviranus, Verm. Schrift. I. p. 47, Taf. VI. fig. 
32, t. t.). These tracheae do not proceed directly 
from the stigmata, but from two large, short trunks 
unobserved by T'reviranus. 
With Gamasus, and Uropoda, there are given 
off, from the two ramified trachean tufts, two un- 
branched tracheae which, remaining of the same 
size, describe a slightly arcuate course along the 
lateral borders of the cephalothorax and terminate 
in caeca at the base of the parts of the mouth. The 
two lateral stigmata of Jvodes have been described 
by Lyonet (loc. cit. p. 288, Pl. XIV. fig. 3, 5), 
Treviranus (Zeitsch. f. Physiol. IV. p. 187, Taf. 
XV. fig. 2, f. f.), and Audouin (Ann. d. Sc. Nat. 
XXY. p. 419, Pl. XIV. fig. 2,q.1r. 8.). For the 
cit. p. 1160). 
With the Solpugidae, whose tracheae 
tracheae of the Acarina, see, moreover, Dujardin 
(Ann. d. Sc. Nat. IIL. p. 16, or Compt. rend. loc. 
It will be difficult, I think, to prove 
the assertion of Dujardin, that, with these animals, 
the trachean system serves exclusively for the act 
of expiration, inspiration being performed wholly 
by the skin. 
2 Duges (Traité d. Physiol. IT. p. 549) is cer 
tainly right in placing the tracheae of the Hydrach- 
nea in the category of Branchiae tracheales, which 
are so widely spread with the aquatic larvae 
of Insecta (see below). 
8 According to dudouin (Ann. d. Sc. Nat. 
XXVITI. 1832, p. 62), the tracheae of Obisium are 
ramified, a statement which I have been unable to 
verify. It has already been stated that the scare 
like fossae on the abdomen of Chelifer have been 
err usly taken for sti fa (§ 298, note 4). 
The tracheae of the Pseudoscorpii are so easily 
seen by the microscope that it is incomprehensible 
how anatomists should have remained so long 
