226 Royal Society. 



vided into four arterial vessels, one of which is given to each of the 

 principal nerves proceeding from the ganglion, and may be traced 

 along with it to a considerable distance. Of these, the vessel situated 

 most posteriorly is again connected with the great median trunk by 

 means of a minute branch, so that the four vessels on each side 

 form, with their trunks, a complete vascular circle above each gan- 

 glionic enlargement of the cord. Besides these, which may be re- 

 garded as the great arterial trunk and vessels conveying the blood 

 directly from the anterior distribution of the heart to the limbs and 

 inferior surface of the body, the author has also discovered a pair of 

 large arterial vessels in each segment, originating directly from the 

 posterior and inferior surface of each chamber of the heart. These 

 vessels he has named the systemic arteries ; and in the Scolopendra 

 he has traced them from the great chamber of the heart, which is 

 situated in the penultimate segment of the body, to their ultimate 

 distribution and ramification in the coats of the great hepatic vessels 

 of the alimentary canal. 



After the blood has passed from the arteries, it is returned again 

 to the heart in each segment of the body by means of exceedingly 

 delicate transparent vessels, which pass around the sides of the seg- 

 ments and communicate with the valvular openings of each cham- 

 ber of the heart at its upper surface, where the valvular openings 

 are situated, not only in all the Myriapoda, but also in tlie Scorpio- 

 nidge. In Scorpions, the circulatory system is more complete and 

 important than even in the Myriapoda. The heart, divided as in 

 Myriapods into separate chambers, is lengthened out at its posterior 

 extremity into a long caudal artery, and gives off a pair of systemic 

 arteries from each chamber, precisely as in the Myriapoda. These 

 arteries not only distribute their blood to the viscera, but send their 

 principal divisions to the muscular structures of the infei'ior and 

 lateral parts of the body, as well as to the pulmonary sacs. At the 

 anterior part of the abdomen, the heart becomes aortic, descends 

 suddenly into the thorax, and immediately behind the brain spreads 

 out into several pairs of large trunks, which are given to the head, 

 and to the organs of locomotion. The posterior of these trunks form 

 a vascular collar around the oesophagus, beneath which they unite, 

 anteriorly, to a strong bony arch in the middle of the thoi'ax, to form 

 the great arterial trunk, or supra-spinal vessel, which conveys the 

 blood to the posterior part of the body, as in the Myriapoda. This 

 vessel passes beneath the transverse bony arch of the thorax, and is 

 slightly attached to it by fibrous tissue, which circumstance pro- 

 bably induced Professor Mviller, who observed this structure in 1828, 

 to x-egard it as a ligament. In its course backwards, along tJie ner- 

 vous cord, this vessel is gradually lessened in size, until it arrives at 

 the terminal ganglion of the cord in the tail, where it is divided into 

 two branches, which take the course of the terminal ner\'cs, and 

 these are again subdivided before they arrive at their ultimate distri- 

 bution. In addition to these parts, the author found a lioUow fibrous 

 structure, which closely surrounds the cord and nerves immediately 

 after they have passed beneath the arch of the thorax. From the 



