446 SANGUIFEROUS SYSTEM. 



wide, sacculated arches, (133. C. c. d,) which embrace the 

 oesophagus, as the corresponding vascular arches which con- 

 nect these two vessels in other annelides and in the entomoid 

 classes. Some branches of the pulmonary arteries which 

 arise from the sides of the sub-gastric vein, are observed to 

 terminate in minute sanguineous vesicles, as in the leech and 

 other annelides, and this vein presents slight enlargements 

 opposite to each ganglion in its course, as in many other 

 species of this class. So that the pale red colour of the 

 blood, the want of a muscular cordiform cavity, the imperfect 

 development of valves, the frequent free anastomoses of 

 the great vascular trunks, and the numerous small pulsating 

 vesicles, seen on the sanguiferous system of the annelides, 

 are conditions in which it resembles also the lymphatic sys- 

 tem of the lowest vertebrated classes. 



The uniformity of the general plan of the circulating sys- 

 tem is still more obvious and more constant in the entomoid 

 than in the helminthoid classes ; and this is especially mani- 

 fest in the position and function of the great median dorsal 

 vessel, the median sub-gastric vein, the cesophageal arches 

 which connect these two greaf vascular trunks, and the 

 lateral vessels most connected with respiration. The least 

 deviation from the ordinary form of the sanguiferous sys- 

 tem of the annelides is found in the myriapods, the most 

 vermiform of all the entomoida ; and it is only in the highest 

 forms of Crustacea that we first arrive at the development of 

 a strong, muscular, capacious ventricle on the great systemic, 

 arterial trunk. The great dorsal vessel in the myriapods is 

 still in form of a narrow, sacculated, pulsating tube, ex- 

 tended along the middle of the whole trunk of the body. In 

 the scolopendra this dorsal muscular vessel or heart begins 

 from the last or caudal segment, and is continued forwards, 

 segmented in appearance, but with little change of calibre, 

 to the second segment behind the head, where it becomes 

 smaller, and is prolonged in the same median line to near 

 the mouth. At the commencement of this narrow anterior 

 portion or aorta, two lateral trunks are given off, to form the 

 usual cesophageal anastomosing arches between the dorsal 

 artery and the median sub-gastric vein. The long narrow 

 dorsal vessel of the myriapods is retained in its situation by 

 the same lateral muscular bands which suspend the heart 

 from the dorsal part of the segments in the other entomoid 



