ARACHNIDS. 563 
the air-slits are obliquely transverse fissures on the ventral plates 
of the abdomen. The uppermost or anterior lip of these slits 
covers in some degree the lower, from which last a membranous 
margin arises, which bears the respiratory organ situated in a 
small cavity. This lung (or gill) consists here, as in spiders, in 
Thelyphonus and Phrynus, of a number of double, very thin plates 
lying upon each other. If now, as is asserted, the air on respira- 
tion really penetrates this chamber so as to fill the spaces between 
the duplicatures, then the name of lung would be justifiable! The 
ordinary position of the stigmata is on the inferior surface of the 
uppermost part of the abdomen. There also AupouIN discovered 
four stigmata in the genus Chelifer that breathes by air-tubes?. 
The Phalangia that also breathe by air-tubes have only a single 
pair of stigmata. In vodes Lyoner and Aupourn found the two 
stigmata furnished with a plate, and upon it, besides a larger open- 
ing, many other smaller ones with a stellate margin®. In spiders 
also the stigma is not always a simple fissure, as in the scorpions, 
but is sometimes closed by a plate perforated like a sieve’. The 
tracheee of arachnids differ often from those of insects by the 
absence of the spiral thread. Usually also they are parcelled in 
bundles, and not divided into branches. However, in Phalangium, 
a system of air-tubes is met with divided into branches and spread 
throughout the body, and provided also with a spiral thread. 
There are two wide principal stems which, running forwards in the 
cephalothorax obliquely towards each other, divide into branches, 
whilst a transverse branch on the inside, behind the thoracic gan- 
glion, forms an arch by uniting with that of the opposite side. In 
the abdomen, behind the stigmata, the lateral principal branches do 
not continue their course, but three smaller branches alone from the 
principal stem penetrate backwards on each side’. 
1 Not on account of respiring in air; for all animals that live in air have not lungs, 
the land-crabs, for example, have gills. The respiratory organs of the Holothwrie, 
on the other hand, although these animals inhale water, are formed after the typus 
of lungs. 
2 Ann. des Sc. nat. XXvuI. 1832. p. 62. 
3 LyoneT Rech. Pl. 6, fig. 5, AUDOUIN, Ann. des Sc. nat. XXV. p. 419, and ToppD’s 
Cyclopedia I. p. 205. 
4 Lyonet, |. 1. Pl. ro, fig. ro. 
5 TREVIRANUS Verm. Schr. I. 8. 32, 33, Tab. Iv. fig. 19, and especially TuLk l. c, 
pp- 327—329. Pl. v. fig. 33. 
36—2 
