ENTEROPNEUSTA HILL. 209 



Behind the branchial region the dorsal nerve cord no longer 

 lies in the bottom of a groove but forms a median ridge, traceable 

 to the posterior extremity of the tail. Just in front of the anus, 

 however, it becomes much less marked, and may even fade away 

 from view. The ventral cord similarly comes to the surface at 

 the end of the branchial region and passes as a median whitish 

 line up to the extreme posterior end of the tail. 



The gonads extend throughout the whole extent of the 

 branchio-genital region up to within a short distance of the 

 anterior liver sacs. 



(2.) Hepatic Region. May reach a length of 27 mm., and a 

 breadth of 5.5 mm. The number of liver sacs in the larger 

 specimens varies from fifty to sixty on each side. The sacs are 

 arranged in two distinct and uniform longitudinal rows. An- 

 teriorly, they commence abruptly, just behind the point of fading 

 away of the genital cushions, while posteriorly they gradually 

 become smaller, and pass over without definite limit into the 

 transverse annulations of the dorsal region of the tail. The most 

 anterior and posterior sacs are colourless in the preserved speci- 

 mens, while the remaining sacs, as well as the ventral portion of 

 the body wall in the hepatic region, are of a light slaty brown 

 colour. The three or four pairs of anterior liver sacs are some- 

 what smaller and thicker antero-posteriorly than the succeeding 

 ones. The latter are simple, markedly compressed antero- 

 posteriorly, and situated close together so that the anterior and 

 posterior faces of the adjacent sacs touch. Each sac has a broad 

 base of attachment corresponding in transverse extent with its 

 free part. The outer ends of the sacs thus do not project freely 

 so as to overhang the lateral body wall, though owing to the 

 lesser transverse breadth of the ventral half of the hepatic region 

 it is not visible when the region is viewed from above. The line 

 of attachment of the outer ends of the sacs is marked on each 

 side by a low longitudinal ridge, continuous in front with the 

 genital cushion. 



(3.) Tail Region. In the largest complete specimen this region 

 is about twice as long as the hepatic region, and measures 5.3 

 cm. in length, with a breadth of 5 mm. In this species, as in 

 P. australiensis, the tail region is characterised by the presence 

 of two dorso-lateral epidermal lines, corresponding to the two 

 underlying ciliated grooves of the intestine. The lines extend 

 from the hepatic region over the anterior two-thirds of the tail, 

 running parallel with the dorsal nerve cord, and about .5 to 

 .75 mm. distant from it. They enclose between them a band-like 

 area of the dorsal body wall, with the dorsal cord running along 

 its middle, and appearing like a direct backward prolongation of 

 the hepatic region. On each side of the nerve cord the area often 



