ANNULATA. 237 



loops upon the upper surface of the intestine, but terminate almost 

 exclusively in a vascular network situated on each side of the abdo- 

 minal cavity near the base of the feet. The principal organs of im- 

 pulsion of the circulating fluid in the tubicolar anellids seem to be 

 the contractile branchiae, which thus combine, as it were, the functions 

 of both heart and lungs. 



Cuvier has noticed the alternate expansion of the branchiae of the 

 Arenicola when they are coloured by the bright red blood, and their 

 contraction, when, by expelling the blood to the internal vessels, they 

 become of a pale grey colour. 



In the Eicnice sanguinea * there is, as in the Terebella, a large and 

 short dorsal vessel, which rests upon the pharyngeal part of the ali- 

 mentary tube, and which communicates, by its posterior extremity, 

 with a vascular ring surrounding the commencement of the intestine. 

 This ring receives two vessels, which run parallel and close together 

 along the dorsal aspect of the intestinal canal, and correspond with 

 the single vessel in the Terebella. The dorso-pharyngeal contractile 

 trunk receives other branches from the parietes of the digestive tube, 

 and a small medio-dorsal cutaneous vessel. It gives off by its an- 

 terior extremity several branches to the head, and others which sur- 

 round the pharynx, and anastomose with the ventral vessel. From 

 this vessel a pair of lateral branches is given off at each ring of the 

 body. These branches immediately dilate, and are bent upon them- 

 selves in a strong sigmoidal curve, appearing at first sight to be simple 

 oval vesicles. They send an ascending branch to the digestive tube, 

 form a small plexus at the base of each of the feet, and penetrate the 

 branchial filaments. The blood is returned from these respiratory 

 organs by transverse veins, which terminate on each side in the dorso- 

 intcstinal vessel of that side. Here, therefore, the respiratory circu- 

 lation is removed further fx-om the dorso-pharyngeal heart, which 

 consequently receives a greater quantity of blood in its arterial or 

 oxygenated state. The principal dynamical organs are, however, the 

 curved dilated sinuses at the bases of the branchiae, which pulsate 

 with strong contractions, and propel the blood at once to the 

 branchiae, the feet, the skin, and the intestine. If we call these 

 pulsatile reservoirs by the name which their functions would claim 

 for them, there will be several hundred hearts in one of these gigantic 

 Nereids. In the Nephthys Homhergi the dorsal vessel is double 

 throughout the greater part of its extent. 



In the Amphinome capillata, which Hunter has heref dissected for 

 the vascular system, this is chiefly remarkable for the size and com- 

 plexity of the branchial plexuses. 



* Edwards, loc. cit, p. 204. f Preps. Nos. 875, 889, and x. pi xiv. fig. 10. 



