ON THE BRITISH ANNELIDA. 185 



testinal commencement of the oesophagus to tlie occiput, and, tortuous and 

 little attaclied, reposing on the upper surface or oesophageal portion of the 

 digestive tube. Coinciding with the whole extent of the intestine-proper in 

 this worm, the anatomist will observe a double vessel along the dorsal-median 

 line, and lodged in parallel apposition in the longitudinal sulcus of the upper 

 surface of the alimentary tube. These two trunks belong to the intestinal 

 system, I'eceiving branches however at numerous points from the integn- 

 nientary veins. In these vessels the blood moves from behind forwards, and 

 mingles in the oesophageal circular vessel with that coming from the lateral 

 intestinal, in which also the blood-stream sets anteriorly, while in the infe- 

 rior intestinal, as in the great sub-ganglionic or ventral, the current sets in 

 the direction of the tail. In this Annelid the branchise are limited to the 

 posterior two-thirds of the body, each branchia consisting of two, three, four 

 or five blood-vessels, according to the species, projecting in a comb-like 

 manner from the dorsal base of each foot. The great heart-like oesophageal 

 dorsal vessel therefore, while anatomically similar, is physiologically very 

 different in this worm and the Terebellce. In the latter species it is exclu- 

 sively a branchial heart, in the former it is indirectly systemic and branchial. 

 It empties itself into the anterior extremity of tiie main ventral trunk, by which 

 the lateral segmental branches are directly supplied to the feet, integument 

 and branchia. 



It was formerly stated ihat Milne-Edwards has described and figured the 

 branchial vessels as ampullated soon after the origin of each from the com- 

 mon trunk, the ampullae being designed to fulfil the function of branchial 

 hearts. These vessels, therefore, according to the representations of Milne- 

 Edwards, are, in Eunice, the exact analogons of those remarkable cardiac 

 vessels (pulmonary hearts) described by M. Duges in the Leech. The ex- 

 istence of these latter vessels has already been demonstrated, beyond doubt, 

 to be altogether imaginary, M. Duges having mistaken for them the curved 

 edges of the reproductive utriculi. According to the author's observations, 

 these vessels in Eunice present nothing approaching to the ampuUas figured 

 in the illustrations of Milne-Edwards. The pouched dilatations are produced 

 by the dissection and exposure to atmospheric stimulus, just as in the Earth- 

 worm the moniliform character of the descending vessel was shown to be 

 caused by the stretching. In Eunice the lateral segmental branches are re- 

 latively large at first, but soon divide into three lesser branches, of which 

 one goes to the foet, the other to the intestine, and the third to the branchiae, 

 from which the blood returns into the dorsal vessel, which in this worm ac- 

 cordingly carries arterial blood. The suddenness of this division favours the 

 imprisonment of a drop of blood in the first stage of the vessels, the drop 

 thus enclosed occasioning a bulged enlargement in this portion of the vessel ; 

 but that this appearance is altogether accidental, the author has repeatedly, 

 and with various kinds of proof, shown to be unquestionable. The blood is 

 admitted into and returned from the branchiae by alternate movements of 

 contraction and dilatation ; these movements are not simultaneous in all the 

 branchiae, but variously and independently in each individually, the afflux 

 into one being synchronous with the efflux of blood from those contiguous. 

 This contractile power is by no means peculiar to these vessels. The motion 

 of the blood in the vessels in every part of the body of the Annelid is effected, 

 not through the agency of uniformly travefling undulatory contractions of 

 their coats, but by complete contractions and relaxations of successive por- 

 tions of the tube ; so that during the instant of contraction, the cylinder ol' the 

 vessel in the part contracting is completely emptied of blood, the sides col- 

 lapsing and meeting in the axis ; and during the period of dilatation, the 



