^310. 



THE ARACUXOIDAE. 



38S^ 



arterial trunk. The anterior of these arteries very soon ramifies, and dis- 

 tributes blood to the feet, the pincers, the cheliceres, and to all the organs 

 in the cephalic extremity. Two of its branches, bending downwards, em- 

 Israce the oesophagus, and then join in a large common vessel called the 

 Supra-spinal artery, which lies upon the ventral cord and accompanies it to 

 the caudal extremity, giving off, in its course, numerous lateral branches.^** 

 The posterior arterial trunk is distributed in like manner to the posterior 

 extremity, and gives off, right and left, numerous branches. The middle 

 chambers of the heart send off, each, laterally, shorter arteries, which are 

 distributed to the neighboring organs. Beside these arteries of the muscles 

 and viscera, these animals have, also, a special Visceral artery, arising from 

 the anterior arterial trunk before it divides into the two branches which 

 form the supra-spinal artery. The visceral artery runs backwards towards" 

 the digestive tube, and sends branches to the liver.'''' The terminal rami- 

 fications of these various arteries are directly continuous, it is said, with a 

 venous system.**^' In this last may be noticed, especially, a Sub-spinal 

 "vein, by which the blood is carried to the pulmonary sacs ; thence to be 

 borne to the heart by speciai vessels. These last open, probably, into a 

 sinus, from which the blood passes into the heart through lateral openings, 

 two of which exist in each of its chambers.! 



4 This supra-spinal artery had been seen, it 

 wuuld appear, by Müller (loc. cit. p. 62, Taf. I. 

 fig. 5, r. r.), but he took it for a ligament. 



5 According to Newport, this visceral artery, 

 \rhich is simple with Androctonux, is divided into 

 two trunks with Buthus. 



(i Newport speaks in his memoir of various an- 

 .aßtomoses occurring between the arteries and veins 

 with Scorpio. But, as he nowhere describes pre- 



cisely this point, and has not distinctly indicated it 

 in his plates otherwise so beautiful, I demur admit- 

 ting that, with the Scorpionidae, the arteries pass 

 directly into the veins, and therefore, that these 

 animals have a system of capillary vessels. This 

 direct communication between these two systems 

 does not exist with the other Arachnoidae, neither 

 with all the other Arthropoda in general.* 



* [ § 310, note 6.] In regard to the question of 

 capillaries with the Scorpionidae, a remark of 

 Blanchard (loc. cit.) may be given. He says, " I 

 have proved with an entire certainty that the blood 

 is distributed in all the cavities of the body, as with 

 all the Articulata, and that it is conveyed to the 

 lungs simply by means of the lacunae. Most of the 

 vessels which arise from the sides of several of the 

 chambers of the heart have appeared to me to be 



pulmono-cardiac vessels, wholly analogous to those 

 we have described with the Araneae." — Ed. 



t [ § 310, end.] For further details on the cir- 

 culatory system of the Arachnoidae, see the memoir 

 quoted above of Blanchard. This naturalist has 

 sought to extend his doctrine of the peritrachean 

 circulation, to the different sections of the Arach- 

 noidae. — Ed. * 



