382 THE ARACHNOIDAE. § 310. 
§ 310. 
With the Arachnoidae, the circulatory organs, when present, are disposed 
in the following 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- 
gal wall by triangular transverse muscles. This heart, which extends also 
into the cephalothorax, sends off from each extremity and from its sides, 
many ramified, 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 effusion, 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. 
ishes from before backwards. 
1See Tulk, loc. cit. p. 249, Pl. IV. fig. 17, H., 
and Treviranus, Verm. Schrift. I. p. 31, Tat. LLL. 
fig. 16, k., and fig. 18.* 
2 For the vascular system of the Araneae, see 
Meckel, in his translation of Cuvier’s Lecons 
d’Anat. comp. Th. IV. p. 261; Treviranus, Bau 
d. Arach. p. 28, Taf. III. fig. 28-31, also his Verm. 
Schrift. L. p. 4, Taf. I. fig.1; Gaede, Nov. Act. Nat. 
Cur. XI. p. 335, Tab. XLIV. fig. 3 (Mygale), and 
Brandt, Mediz. Zool. II. p. 89, Tat. 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 
*{ § 310, note 1] Blanchard (loc. cit. Ann. 
d. Sc. 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 esophagus. At the base of this 
aorta the ophthalmic artery is given off, which 
bifurcates behind the cyes. From this portion of 
ihe heart also pass off branches to the stomach. 
This naturalist declares the existence here of his 
peritrachean system, which, together with the heart, 
he says he has injected through the lacunae. — 
Eb. 
It has eight chambers whose size dimin- 
At each extremity itis prolonged into an 
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 (Considérat. &c. p. 345, and Traité d’Anat. 
comp. II. p. 251), and since confirmed by Grant 
(Outlines, &c., p. 452) and Grube (loc. cit. p. 
300). 
3 Treviranus (Bau d. Arachn. p. 9, Taf. I. fig. 
7), and Miler (loc. cit. p. 38, Taf. IL. 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, Pl. XIV. XV., or Froriep’s neue 
Notiz. XX XIX. p. 81, fig. 38-40. = 
t[ § 310, note 2.) According -to Blanchard 
(loc. cit.), the blood, in the Araneae, passes to the 
respiratory organs, which it penetrates by a kind 
of infiltration ; from the lacunae of the walls of the 
lungs it is taken 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 which have 
both lungs and tracheae, such as Segestria, Dys- 
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 peritrae 
chean system of circulation. — Ep. 
