886 THE ARACHNOIDAE. <?. 313 



§ 313. 



The Lungs of the Arachnoidae consist of round sacs situated near the 

 lower surface of the abdomen and communicating, externally, by transverse 

 fissures. Their internal surface has numerous thin solid lamellae, triangu- 

 lar or rhomboidal, and connected together like the leaves of a book. By 

 reflected light these lamellae have the same silvery lustre as the tracheae, 

 although, seen by direct light, they appear of a deep-violet, nearly black 

 color. Each of these is formed by a membranous fold, between the two 

 leaves of which the air enters from the general cavity of the lung and is 

 divided into very minute portions. No traces of blood-vessels have been 

 found in these Pulmonary lamellae. It is therefore very probable that the 

 blood of the pulmonary arteries is effused into the parts surrounding the 

 lungs, and in this way bathes the lamellae. ^^* 



With the Scorpionidae, the four anterior segments have, each, on their 

 under surface, a pair of stigmata. These animals have eight pulmonary 

 sacs, in each of which there are twenty fan-shaped lamellae.'-^ The genus 

 Phrymis has only two pairs of pulmonary sacs, the stigmata of which are 

 placed between the first and second, and the second and third abdominal 

 segments. But each sac has eighty lamellae. '^^ With the Araneae, there 

 are only two lungs occupying the base of the abdomen. The number of 

 their lamellae is considerably less than in the preceding groups. But with 

 the Mygalidae only, there is a second pair of lungs directly behind the first. 

 The place occupied by these organs, is indicated, with the Ai'aneae, by a 

 triangular horny plate, at the posterior border of which is a stigma.*''^ 



1 These organs, with which no motions have been act. 1843, p. 295, PI. XIV.) is probably mistaken in 



discovered, have l)een called Branchiae by many saying that unnucleated cells and a very fine 



Zootomists. But the name of Lungs is very ap- capillary net-work e.xist between these plates, and 



propriate since the respiration is atrial and not that the net-work arises from a branch of the pul- 



aquatic. monary artery situated on the free border of each 



^ For the lungs of the Scorpionidae, see Meckel, lamella. 



Translat. of LeQons d. Anat. comp, of Cuvier, Th. 3 See F'an der Hoeven, Tijdsch. loc. cit. 



IV. p. 291 ; Treviranus, Bau d. Arach. p. 7, Taf. * The lungs of the Araneae have been studied 



I., and Beobacht. aus d. Physiol, p. 25, fig. 40-42 ; by Meckel (Translat. LeQons d'Anat. comp, of 



Müller, Isis, 1828, p. 708, Taf. X. fig. 1-3, and in Cuvier, loc. cit. p. 290), Treviranus (Bau d. 



Meckel's Arch. loc. cit. p. 39, Taf. II. fig. 11-13. Arachn. p. 24, Taf. II. and Beobacht. &c. p. 29, fig. 



Müller has very correctly, and in the above-men- 43-47), Gaede, Nov. Act. Nat. Cur. XI. p. 335, 



tioued manner, understood this respiratory appara- (Mygale) ; but especially by Müller (Isis, 1828, p. 



tus, while, on the other hand, Treviranus and 709, Taf. X. fig. 4^). See also Menge, loc. cit. 



other anatomists, think that the air, instead of p. 21, Taf. I. fig. 6-9. I am unable to say by 



entering between the leaves of the pulmonary what means the l)lood returns to the heart, whether 



lamellae, passes over their external surface, and Vjy a direct course, or, more or less circuitously 



that the blood penetrates between the two plates through the interstices of the parenchyma, for 



«omposing the leaves. Newport (Philos. Trans- there are no veins. 



/cer''s Zeitsch. 1849, I. p. 246) who, contrary to view put forth together with the general doctrine 



Jilanchard, advances the view that these organs that the pulmonary sacs of the Arachnoidae are, 



are only a form of tracheae, infra-formed, and likewise, but modifications of the tracheal type, 



which are without the spiral filament, because has many facts deserving the attention of anato- 



their simple, unbranched condition does not re- mists, and especially the developmental relations 



quire, like the ramose tracheae, a spring-like of the spiral thread as observed in the embryos of 



atrunture, to prevent them from collapsing. This these animals. — Ed. 



