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 

 largin arises, which bears the respiratory organ situated in a 

 all 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- 

 ion really penetrates this chamber so as to fill the spaces between 

 ;he duplicatures, then the name of lung would be justifiable 1 . The 

 rdinary position of the stigmata is on the inferior surface of the 

 :ppermost part of the abdomen. There also AuDOUiN discovered 

 ? our stigmata in the genus Chelifer that breathes by air-tubes 2 , 

 'he Phalangia that also breathe by air-tubes have only a single 

 iair of stigmata. In Ixodes LYONET and AUDOUIN found the two 

 itigmata furnished with a plate, and upon it, besides a larger open- 

 ig, many other smaller ones with a stellate margin 3 . In spiders 

 the stigma is not always a simple fissure, as in the scorpions, 

 .t is sometimes closed by a plate perforated like a sieve 4 . The 

 L ea3 of arachnids differ often from those of insects by the 

 .bsence of the spiral thread. Usually also they are parcelled in 

 lundles, and not divided into branches. However, in Phalangium, 

 system of air-tubes is met with divided into branches and spread 

 .roughout the body, and provided also with a spiral thread. 

 iere are two wide principal stems which, running forwards in the 

 ihalothorax obliquely towards each other, divide into branches, 

 list a transverse branch on the inside, behind the thoracic gan- 

 ion, forms an arch by uniting with that of the opposite side. In 

 .e abdomen, behind the stigmata, the lateral principal branches do 

 it continue their course, but three smaller branches alone from the 

 incipal stem penetrate backwards on each side 5 . 



1 Not on account of respiring in air ; for all animals that live in air have not lungs, 



land-crabs, for example, have gills. The respiratory organs of the ffolotkurice, 



the other hand, although these animals inhale water, are formed after the typus 



lungs. 



8 Ann. des Sc. nat. xxvn. 1832. p. 62. 



3 LYONET Reck. PI. 6, fig. 5, AUDOUIN, Ann. des Sc. nat. xxv. p. 419, and TODD'S 



lia I. p. 205. 



4 LYONET, 1. 1. PI. 10, fig. 10. 



5 TREVIRANUS Verm. Schr. I. s. 32, 33, Tab. rv. fig. 19, and especially TULK 1. c. 

 . 327 329. PL v. fig. 33. 



362 



