^84 



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 Opilienina, 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 in 

 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 

 fi'om 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.*'^* With the Solpugidae, whose tracheae 



1 See Doyire, loc. cit. p. 316. 



2 See Qiiatrefas^es, loc. cit. p. 76. 



3 Demodex, Snrcoptes, Acarus, &c. 



1 With Trombidium, there arise two simple 

 and very distinct trachean tufts from the two 

 8tif,'mata situated behind the second pair of legs 

 {Treviranus, Verm. Schrift. I. p. 47, Taf. VI. fig. 

 32, t. t.). Tticse tracheae do not proceed directly 

 from the stiumata, but from two large, short trunks 

 unobserveil iiy Treviranus. 



With (jnma/ius, and Uropnda, there are given 

 off, from tlie two ramified trachean tufts, two un- 

 branched triicticae wtiich, remaining of the same 

 size, descril)e a sUglitly arcuate course along tlie 

 lateral borders of the ceplialotliorax and terminate 

 in caeca at tlie l)ase of tlie jiarts of the mouth. The 

 two lateral stigmata of Ixodm have been descrilied 

 by Lyonet (loc. ell. )). 2.SH, I'l. XIV. fig. 3, 5), 

 Treviranux (Zeitsch. f. I'liysiol. IV. p. ]87, Taf. 

 XV. fig. 2, /"./.), and Ando'iiin (,\.iin. d. Sc. Nat. 

 XXV. p. 419, PI. XIV. lig. 2, (1. r. s.). for the 



tracheae of the Acarina, see, moreover, Dujardin 

 (Ann. d. Sc. Nat. III. p. 16, or Compt. rend. loc. 

 cit. p. 1160). 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 Dusia (Traits d. Physiol. IT. p. 549) is cer- 

 tainly right in i)lacing the tracheae of the Hydrach- 

 nea in the category of Branchiae trai-hea/ex, which 

 are so widely sjiread with the aquatic larvae 

 of Insecta (see below). 



•J According to Atidouin (Ann. d. Sc. Nat. 

 X.XVII. 1832, p. 62), the tracheae of Obisium are 

 ramified, a statcinrnl which I have been unable to 

 verify. It has alri-ady been stated that the scar- 

 like fossae on the abdmnen of CheLifer have been 

 erroneously taken for stigmata ( § 298, note 4). 

 The tracheae of the Pseudoscorpii are so easily 

 seen by the microscope that it is incomiirehensible 

 how anatomists should have remained so long. 



