386 



THE ARACHNOIDAE. 



<5>313. 



§ 313. 



The Lunss 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 eifused 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 

 Phrynus 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 Araneae, by a 

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



1 These organs, with which no motions have been 

 discovered, have been called Branchiae by many 

 Zootomists. But the name of Lungs is very ap- 

 propriate since the respiration is aerial and nut 

 aquatic. 



^ For the lungs of the Scorpionidae, see Meckel, 

 Translat. of Lecjons d. Anat. comp. of Cuvier, Th. 

 IV. p. 291 ; Treviranus, Bau d. Arach. p. 1, Taf. 

 I., and Beobacht. aus d. Physiol, p. 25, fig. 40-42 ; 

 Miiller, Isis, 1828, p. 708, Taf. X. fig. 1-3, and in 

 MeckePs Arch. loc. cit. p. 39, Taf. II. fig. 11-13. 

 Miiller has very correctly, and in the above-men- 

 tioned manner, understood th's respiratory appara- 

 tus, while, on the other hand, Treviranus and 

 other anatomists, thinli that the air, instead of 

 entering between the leaves of the pulmonary 

 lamellae, passes over their external surface, and 

 that the blood penetrates between the two plates 

 composing the leaves. Newport (Philos. Trans- 

 fer's Zeitsch. 1849, I. p. 246) who, contrary to 

 Blanchard, advances the view that these organs 

 are only a form of tracheae, infra-formed, and 

 which are without the spiral filament, because 

 their simple, unbranched condition does not re- 

 quire, like the ramose tracheae, a spring-like 

 structure, to prevent them from collapsing. This 



act. 1843, p. 295, PI. XIV.) is probably mistaken in 

 saying tliat unnucleated cells and a very fine 

 capillary net-work exist between these plates, and 

 that the net-work arises from a branch of the pul- 

 monary artery situated on the free border of each 

 lamella. 



3 See Van der Hoeven, Tijdsch. loc. clt. 



4 The lungs of the Araneae have been studied 

 by Meckel (Translat. Lemons d'Anat. comp. of 

 Cuvier, loc. cit. p. 290), Treviranus (Bau d. 

 Arachn. p. 24, Taf. II. and Beobacht. &c. p. 29, fig. 

 43-47), Qaede, Nov. Act. Nat. Cur. XI. p. 335, 

 (Mysa/e) ; but especially by Mailer (Isis, 1828, p. 

 709, Taf. X. fig. 4-6). See also Menf^e, loc. cit. 

 p. 21, Taf. I. fig. 6-9. I am unable to say by 

 what means the blood returns to the heart, whether 

 by a direct course, or, more or less circuitously 

 through the interstices of the parenchyma, for 

 there are no veins. 



view put forth together with the general doctrine 

 thai the pulmonary sacs of the Arachnoidae are, 

 Ukewise, but modifications of the tracheal type, 

 has many facts deserving the attention of anato- 

 mists, and especially the developmental relations 

 of the spiral thread as observed in the embryos of 

 these animals. — Ed. 



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