80 ANATOMY OF THE EISTOPLA. 



situated in a layer of transparent elastic tissue intervening between this organ and the digestive 

 tract. At the ganglionic region the vessels which go to form the cephalic arch pass below the 

 commissures, and unite in front beneath the channel of the snout. In N Neesii there are three 

 main longitudinal trunks as in A. lactifloreus ; but it can be observed that the lateral communi- 

 cate with the central, as in Lineus, by transverse branches, which, however, are proportionally 

 smaller. Whether such anastomoses occur in the pale Amphiporince is thus an open question ; 

 but they are distinct enough in this species. Two lateral trunks only could be discovered in 

 Nemertes carcinophila (Plate XIV, fig. 4, r), which unite by a very short loop just in front of 

 the commissures. This arch (I) is distinguished from the ordinary arrangement by its not 

 extending forward into the tissues of the snout. The lateral vessels are not so clear or well 

 defined as in A. lactifloreus and Tetrastemma, and possess internal transverse bands or partial 

 septa in front ; while the fluid circulating therein has a few clear granules, as in N Neesii 

 and others. The contractions in the lateral trunks are very vigorous, and even a minute central 

 vessel could not have been passed over if a trace of such had existed. 



The course of the circulation, so far as observed, is as follows : — Posteriorly a gentle 

 contraction from behind forward drives the contained fluid along the great central vessel to the 

 front, where it is forced through the anastomotic into the lateral vessels and the cephalic 

 arch. Each lateral trunk swells with the wave, and the fluid then proceeds to the posterior 

 end to enter the median, as before-mentioned. In addition to the stream poured into the lateral 

 trunks, another passes into the cephalic arch by the vessel on each side, and the counter-currents 

 must meet and commingle, returning again during the diastole of the central vessel. I have not 

 made out any branches in the British species except in N. Neesii ; but this is a somewhat 

 difficult task, on account of the transparency of the vascular medium and channels. 



In many species the fluid contained in these vessels is transparent and homogeneous. M. de 

 Quatrefages, however, found corpuscles in his Folia bembix, Professor Keferstein small oval discs 

 in the reddish blood of his Borlasia splendida (Ampkiporus spectabilis } Quatref.), and I have seen 

 in N Neesii minute granular corpuscles, but both they and the fluid are colourless. Minute 

 colourless globules also occur in the blood of A. pule her. 



The ideas of M. Duges with regard to the circulation in these animals were rather indistinct, 

 though he discovered certain vessels. In his figure he represents a median and no less than 

 three lateral trunks on each side, and he further joined the ganglia to this system under the 

 character of pellucid pouches communicating with the arcade (cephalic arch). The latter he 

 transformed into a complex series of vessels, which need not be particularly described. He thus 

 confounded the nervous and circulatory systems. The first point to be noticed in the descriptions 

 of M. de Quatrefages is the statement, that the lateral trunks pass through the cephalic 

 diaphragm — a structure which has not been seen. He is slightly in error also when he states 

 that the median vessel lies immediately under the subcutaneous muscles. The arrangement 

 shown in his two sections of Borlasia anglia cannot apply to this group. I have not been able 

 to verify the elaborate curves which this author gives each anastomotic division of the central 

 vessel anteriorly, and which may be described as first forming a loop behind the ganglion, with 

 its curve directed outwards, and a second inversely curved round the anterior border — in its 

 passage to join the lateral, which is scarcely bent inwards at all, but occupies a space where 

 no vessel occurs in the British forms. The mere shortening of the anastomotic will not 

 retrieve this anatomical error. The cephalic arch is also placed otherwise than "immediatement 



