382 



THE ARACHNOIDAE. 



«§> 310. 



§ 



310. 



With the Arachnoidae, the circulatory organs, when present, are disposed 

 in the Ibllowing manner : 



With the Phalangidae, they consist only of a Dorsal Vessel, -which is 

 three-chambered, and attenuated at both extremities/*' 



With the Araneae, the dorsal vessel is fusiform, and has many constric- 

 tions. It is situated principally in the abdomen, being attached to its dor- 

 sal wall by triangular transverse muscles. This heart, which extends also 

 into the cephalothorax, sends off from each extremity and from its sides, 

 many ramihed, vascular canals, which are certainly Arteries. 



The two of these last arising directly behind the peduncle of the abdo- 

 men, are distributed to the pulmonary sacs, while those following penetrate 

 chiefly the liver. All these vessels gradually disappear in the parenchyma 

 of the body, and the blood, after its efiusion, continues to circulate in the 

 lacunae, and, without the intervention of veins, is returned to the heart, or 

 more properly into the blood-reservoir which corresponds to the dorsal 

 sinus of the Crustacea. Thence it enters the heart through its lateral, 

 valvular openings.'-' 



The vascular system is most highly developed with the Scorpionidae. 

 For, here, not only is there an articulated Heart and Arteries, but also a 

 "Venous system.® The cylindrical heart whose walls contain transverse 

 and longitudinal muscular fibres, is retained in place between the dia- 

 phragm of the cephalothorax and the last abdominal segment, by several 

 transverse triangular muscles. It has eight chambers whose size dimin- 

 ishes from before backwards. At each extremity it is prolonged into an 



1 See Tulk, loc. cit. p. 249, PI. IV. fig. 17, H., 

 and Treviranus, Verm. Scbrit't. I. p. 31, Taf. III. 

 fig. 16, k., aud (ig. 18.* 



2. For the vascular system of the Araneae, see 

 Meckel, in his translation of Cuvier's LeQons 

 d'Auat. cump. Th. IV. p. 261 ; Treviranus, Bau 

 d. Arach. p. 28, Taf. III. fig. 2S-31, also his Verm. 

 Schrift. I. p. i, Taf. I. fig. 1; Gaede, Nov. Act. Nat. 

 Cur. XI. p. 335, Tab. XLIV. fig. 3 {Mygale), and 

 Brandt, Mediz. Zool. II. p. 89, Taf. XV. fig. 16, 

 17. See also Duges (loc. cit. p. 181), who has been 

 unable to find the venous system with the Araneae, 

 but, at the same time, traced the heart even into 

 the cephalothorax. Wasmann (loc. cit. p. 16, fig. 

 24), on the other hand, affirms that he has observed, 

 with Mygale, venous trunks which entered the 



heart above the points of origin of the arteries. 

 The analogy between the heart of Crustacea and 

 of Araneae has been especially pointed out by 

 Straus (Considerat. &c. p. 345, and Traite d'Anat. 

 comp. II. p. 251), and since confirmed by Grant 

 (Outlines, &c., p. 452) and Grube (loc. cit. p. 

 300).t 



3 Treviranus (Bau d. Arachn. p. 9, Taf. I. fig. 

 7), and Muller (loc. cit. p. 38, Taf. II. fig. 22), 

 were acquainted with only the heart and larger vas- 

 cular trunks of the Scorpionidae ; but Newport 

 has given of the blood system of these Arachnoidae 

 a complete and masterly description accompanied 

 with very beautiful figures ; see Philos. Trans. 

 1843, p. 286, I'l. XIV. XV., or Froriep's neue 

 Notiz. XXXIX. p. 81, fig. 38-40. 



* [ 5 310, note 1.] Blanchard (loc. cit. Ann. 

 d. So. Nat. XII. 1849, p. 333) has extended our 

 knowledge of the circulatory system of this family. 

 The dorsal vessel terminates behind in a small ves- 

 sel which runs to the extremity of the body. In 

 front it passes into an artery of considerable size, 

 which passes under the brain and sends off small 

 branches to the oesophagus. At the base of this 

 aorta the ophthalmic artery is given off, which 

 bifurcates behind the eyes. From this portion of 

 the heart also pass off branches to the stomach. 

 This naturalist declares the e.\istence here of his 

 peritrachean system, which, together with the heart, 

 he says he has injected through the lacunae. — 



t [ § 310, note 2.] According to Blanchard 

 (loc. cit.), the blood, in the Araneae, passes to the 

 respu-atory organs, which it penetrates by a kind 

 of infiltration ; from the lacunae of the walls of the 

 lungs it is tiiken to the heart by means of the pul- 

 mono-cardiac vessels which have hitherto been 

 taken for arteries. There are six pairs with Epeira 

 diadema. But with those Araneae wliick have 

 both lungs and tracheae, such as Segestria, Dya- 

 dera, &c., there is some modification, although the 

 arterial system resembles that of the Araneae 

 essentially pulmonary ; the heart is smaller and 

 has fewer chambers, and the true arteries seem to 

 lose their importance and give place to the peritra- 

 chean system of circulation. — Ed. 



