138 LECTURE XI. 



tine, where, with the absorbent veins of that canal, it returns again 

 into the dorsal vessel. In some other species of Terebella, as the 

 Ter. cotichilega, the lateral branches of the ventral trunk do not 

 ascend in loops upon the upper surface of the intestine, but terminate 

 almost exclusively in a vascular network situated on each side of the 

 abdominal cavity near the base of the feet. The principal organs of 

 impulsion of the circulating fluid in the tubicolar anellides 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 Eunice sanguined * 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 anterior 

 extremity several branches to the head, and others which surround 

 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 themselves 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- 

 intestinal vessel of that side. Here therefore the respiratory circula- 

 tion is removed further from the dorso-pharyngeal heart, which con- 

 sequently 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, tlie skin, and the intestine. If we call these pulsatile re- 

 servoirs by the name which their functions would claim for them, 

 there will be several hundred hearts in one of these gigantic Nereids. 



In the Amphinome capillata, which Hunter has here |- dissected for 



* Edwards, loc. cit. p. 204. f I'reps. Nos. 875. 889. 



