884 THE ARACHNOIDAE. §§ 311, 312. 



CHAPTER VII. 



RESPIKATORY 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 pidmonariae . 

 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 

 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.''^* With the Solpugidae, whose -tracheae 



1 See Doyere, loc. cit. p. 31(i. tracheae of the Acarina, see, moreover, Dujardin 



2 See Quatrefaffes, loc. cit. p. 76. (Ann. d. So. Nat. III. p. 16, or Compt. rend. loc. 



3 Demodex, Sarcoples, Acarus, &c. cit. p. 1160). It will be diflicult, I think, to prove 

 1 With Trombidium, there arise two simple the assertion of £)!yar(im, that, with these animals, 



and very distinct trachean tufts from the two the trachean system serves exclusively for the act 



stigmata situated behind the second pair of legs of expiration, inspiration being performed wholly 



(Treviranus, Verm. Schrift. I. p. i1, Taf. VI. fig. by the skin. 



32, t. t.). These tracheae do not proceed directly -' Dui^cs (Traits d. Physiol. II. p. 549) is cer- 



from the stigmata, but from two large, short trunks tainl'y right in placing the tracheae of the Hydrach- 



unobserved by Treviranus. nea in the category of Branchiae tracheales, which 



With Gamasus, and Uropoda, there are given are so widely spread with the aquatic larvae 



off, from the two ramified trachean tufts, two un- of Insecta (see below). 



branched tracheae which, remaining of the same 3 According to Audouin (Ann. d. Sc. Nat. 

 size, describe a slightly arcuate course along the XXVII. 1832, p. 62), the tracheae of Obisium are 

 lateral borders of the cephalothorax and terminate ramified, a statement which I have been unable to 

 in caeca at the base of the parts of the mouth. The verify. It has already been stated that the scar- 

 two lateral stigmata of iarorffls have been described like fossae on the abdomen of Chelife.r have been 

 by Lyonet (loc. cit. p. 288, PI. XIV. fig: 3, 5), erroneously taken for stigmata (§"298, note 4). 

 Treviranus (Zeitsch. f. Physiol. IV. p. 187, Taf. The tracheae of the Pseudoscorpii are so easily 

 XV. fig. 2, /./.}, and Audouin (Aim. d. Sc. Nat. seen by the microscope that it is incomprehensible 

 XXV. p. 419, PI. XIV. tig. 2, q. r. s.). For the how anatomists should have remained so long 



