igoS.] J. Stephenson: The Anatomy of some Aquatic OUgochœta. 279 



in the anterior third of the stomach, and an '' antiperistaltic " (postero-anterior) 

 movement through the whole of the alimentary tract behind this, which, meeting 

 the direct (antero-posterior) movement in the stomach-walls, overcomes the latter 

 and then continues forward. 



The ventral hlood-vessel is intimately connected with the alimentary canal for 

 the greater part of its extent ; it is a wide tube, nearly as wide as the lumen of the 

 alimentary tract itself {cf. fig. 55), non-contractile, bifurcating posteriorly to the 

 buccal funnel, and thence continued forwards as two commissural vessels in the 

 funnel- wall, meeting dorsally at the base of the cerebral ganglion. There is in the 

 intestinal region no separate dorsal vessel, but a system of lacunae or sinuses in the 

 intestinal wall ; this system does not seem usually to be independently contractile, 

 apart from the ' ' antiperistaltic ' ' contractions of the intestinal wall ; but on one 

 occasion, in a very sluggish, somewhat contracted animal, where the '' antiperistaltic" 

 contractions were entirely in abeyance for some time, the sinuses in the intestinal 

 wall kept up a rhythmical postero-anterior contraction of their own. The system 

 of sinuses extends through the stomach also ; but here a distinct though small dorsal 

 vessel makes its appearance as an interrupted cavity much smaller in its vertical 

 calibre, as seen from the side, than the well-marked ventral vessel. In the 

 œsophageal region there is, dorsally situated, a series of large, vacuole-Iike chambers, 

 or a single chamber traversed by strands or septa, which extends forwards to just 

 behind the first setal bundles; this, probably formed posteriorly by the union of the 

 dorsal vessel and sinus system of the stomach, is continued forwards as a definite 

 blood-vessel as far as the base of the cerebral ganglion ; it is contractile as far as 

 this latter point, usually in a postero-anterior direction, the contractions at times 

 appearing to be a continuation forwards of the '' antiperistalsis" of the alimentary 

 tube, while at other times they are quite unconnected with the rhythm of the latter. 

 On two occasions the contractions of this part of the vascular system were certainly 

 not definitely postero-anterior, and appeared to be rather in the reverse (antero- 

 posterior) direction. 



The hlood is colourless, and contains no corpuscles. 



The nephridia usually begin in the space between the first and second setal 

 brmdles ; on one occasion one only could be defined in this place, and on two occa- 

 sions they were absent here on both sides, beginning between the second and third setal 

 bundles. They are always present here and in the succeeding space, but posteriorly 

 there are slight variations in their distribution, the fourth, or fifth, or sixth setal 

 interspace being sometimes destitute of nephridia. The hindmost segments seem 

 never to have nephridia ; I have not noted their occurrence behind the seventh setal 

 bimdles. They open anteriorly by a large ciliated funnel ; and appear to have an 

 attachment to the wall of the alimentary canal. 



The cerebral ganglion is rounded in front, markedly indented behind. As is the 

 rule in the genus, it is closely connected to the surface epithelium, appearing in a 

 lateral view (fig. 54, e.g.) merely as a local thickening of the latter. No nerve cords 

 or commissures were discoverable. 



