MAGELONA. 221 



regarded as oesophageal, whilst that having a smooth outline and internally granular 

 glandular tissue projecting in conical elevations, which in section present a dendritic or 

 radiated appearance, may be stomachal. At the ninth segment the circular muscular coat 

 is much thickened, the basement-tissue increased, and the glandular lining more consistent. 

 In the next region of the body the entire canal assumes the soft, greenish glandular con- 

 dition characteristic of the intestine and its chloragogenous coat. It diminishes toward 

 the tip of the tail and ends in a dorsal anus, the cilia in the terminal region being largely 

 developed. 



The circulation in Magelona is remarkable for the presence of pinkish corpuscles in 

 the blood. Two dorsal vessels arise at the posterior end from a bifurcated ventral and 

 pass forward, closely connected by a median raphe (Fig. 124) on the dorsal arch of the 

 alimentary canal, receiving in each segment a large branch from the ventral and numerous 

 twigs from the alimentary canal, till they reach the posterior part of the tenth segment. 

 There the walls are supplied with a powerful muscular layer which enables them to 

 perform the functions of contractile chambers or "hearts." These chambers dilate, and 

 then by vigorous systole drive the blood forward in a swift stream along the single anterior 

 dorsal vessel which terminates in a branch to each tentacle, the stream being sent into 

 each simultaneously. The blood courses along the afferent trunk next the smooth margin 

 of the organ, and enters an extensive series of rudimentary capillaries which join the 

 afferent trunk. Toward the tip of the tentacle the afferent vessel breaks up into numerous 

 branches which join to form the vein, which is larger than the afferent vessel and lies next 

 the papillose border. The purified blood returning from the tentacles curves forward into 

 the snout to the tip of the lateral muscles, and, bending round, constitutes the vein which 

 returns the blood to the ventral system. 



The lateral trunks— external and internal— spring from the returning cephalic vessels, 

 and in the first segment of the body form numerous transverse anastomoses with each 

 other, so that a great plexus exists in connection with the proboscidian system, and finally 

 this rete mirabile terminates in the single ventral vessel of the ninth segment, the outer 

 lateral, in bending inward to the median line, forming slight pouches or dilatations 

 (analogous to those of the dorsal vessels) which pour the blood backward at short intervals 

 and simultaneously with the forward jets of the dorsal " hearts." When the anterior 

 region of the body is in repose it is difficult to say in what direction the current in these 

 vessels proceeds. It seems to disappear in contraction through the transverse vessels, and 

 does not go in a continuous stream backward. In ordinary circumstances a large current 

 flows backward in the sheath of the dorsal vessel, and thus in the opposite direction to that 

 in the vessel itself. The whole anterior region, indeed, is a great vascular plexus akin to 

 that in the Nemerteans. By-and-by the external vessels disappear, and the internal 

 lateral vessels unite to form the single median ventral trunk which terminates at the tail 

 by bifurcating and turning upward to constitute the dorsal trunks. 



The general arrangement of the circulation in the posterior region may be illustrated 

 by the condition in the eighteenth segment of the region. A large vessel goes outward 

 from the ventral trunk at each dissepiment and trends under the body-wall to the posterior 

 part of the segment, thus necessarily passing the bristle-tuft. It then forms a loop, returns 

 to the dissepiment, and bends inward to join the dorsal vessel. Under favourable circum- 



