220 PSKUDOBONKLLIA, A NEW ECH1UROID GENUS, 



viridis. Anteriorly in the region of the setse, the ventral vessel 

 is much narrower. Between the setae, it passes vertically upwards 

 and then bifurcates, the branches passing around the oesophagus 

 in whose muscular walls they lie; they enter the proboscis, and, 

 passing forwards in close connection with the corresponding pro- 

 boscis nerve to which they each lie ventrally, travel to the 

 anterior end (Plate ix., fig. 5). Still closely associated with the 

 nerve, they each enter a bifurcation of the proboscis, to the 

 extremity of which they extend, then turn back, meeting in the 

 middle to complete the circumoasophageal vessel. Along their 

 whole length they are suspended in the prolongations of the 

 ccelome already described. From the mid-dorsal region of the 

 circum-cesophageal vessel a dorsal bloodvessel is given oft', 

 travelling down the middle of the proboscis surrounded by a 

 tissue which, as already stated, appears to be nervous. This 

 dorsal vessel breaks up into capillaries in the vicinity of the 

 oesophagus. 



Anal trees. — The anal glands or posterior nephridia are repre- 

 sented by two small, tuft-like masses situated one on each side of 

 the posterior end of the intestine (Plate ix., fig. 7). Each consists 

 of a mass of very delicate, simple, cylindrical tubes opening sepa- 

 rately into the rectum, whose walls in this region are thickened, 

 while rather prominent ridges of tissue project into its lumen, 

 giving the tube a star-like appearance in section. This is perhaps 

 due to the presence of well-marked circular (sphincter) and longi- 

 tudinal bundles of muscle fibres. The tubules are approximately 

 circular in section with an irregular lumen. They consist of a 

 single layer of elongate epithelial cells. Near its free end each 

 tubule becomes narrowed before opening into the ccelome by a 

 slightly dilated funnel fringed with long cilia (Plate x., figs. 13, 

 14, 15). The nephridia thus differ from those described in 

 various species of Bonellia, in that the funnels are simple, un- 

 branched tubes which open directly into the rectum, instead of 

 into a large vesicle on -each side. 



The Ovary. - The mesenteric strands of muscular tissue which 

 maintain the posterior portion of the rectum in position are very 

 well developed and form the basis of the ovary (Plate ix., fig. 2), 



