214 PROF. W. B, BEXHAM OX AQUATIC [Nov. 3, 



cesopliagus, in the hinder part of segment ii. ; it thickens out 

 considerably, right and left, in segment iii., forming a somewhat 

 quadrangular organ, looking — in an entire specimen — like a 

 pharynx. The walls of this organ are comparatively thin, some- 

 what folded laterally, and lined by tall, columnar, cihated epi- 

 thelium*, which is surrounded by a very feebly developed 

 muscular layer ; the floor is raised into a ridge in the median 

 line. The structure recalls that described by Nasse for Tubifex f. 

 In segment iv. the oesophagus, retaining the same structure, 

 diminishes in size vertically, but is still rather wide laterally. 



The chloragogen ceUs — which are quite pale — begin in seg- 

 ment vi. 



In the eighth segment (PI. XXY, fig. 12) the oesophagus passes 

 into the intestine. The former region reaches into the first half of 

 the segment, then suddenly, at about the middle of the segment, 

 dilates to about three times its former size. The epithelium, 

 anteriorly high, is there quite low, and the cells contain blackish 

 granules. The chloragogen granules have been dissolved out in 

 the sections, but these dark intestinal granules remain. 



The intestine is greatly dilated in each segment, and constricted 

 by the successive septa. 



The Vascular System. — In the oesophageal region the dorsal 

 vessel is free from the wall of the gut, as is the case in Oligochseta 

 generally. In the eighth segment it presents an arrangement 

 which appears to be, in its details, unique (PL XXY. fig. 12). 

 In the anterior (oesophageal) moiety of segment viii. the vessel 

 becomes very muscular, and at the junction of oesophagus with 

 intestine the dorsal vessel bifurcates ; each branch, one on either 

 side, passes downwards and backwards, along the line of union of 

 oesophagus with intestine, to join the ventral vessel. This con- 

 necting vessel adheres closely to the wall of the gut, lying in a 

 furrow therein, and has a very thick muscular wall (PL XXY, 

 fig. 13) ; it is, however, not specially dilated in the way that the 

 " lateral heart " of Tubifex is, and, further, it is connected with 

 the dorsal vessel, and not with the supra-intestinal as is the case 

 in other Tubificids \yide Stole ; Beddard, Monog. p. 240]. 



Behind the eighth segment, the dorsal vessel comes to lie below 

 the peritoneal cells, above the gut-wall, in the usual way. 

 Anteiiorly to the eighth segment there is a " supra-intestinal " 

 vessel adhering to the oesophageal roof ; it passes forwards through 

 several segments, but I did not ascertain how far it reaches. 



In the intestinal region the vascular network on the gut-wall 

 is connected with the dorsal vessel ; while in the oesophageal 

 region it is, as usual, connected with the supra-intestinal vessel. 



Commissural vessels, undulating along the inner surface of the 

 body- wall for the whole length of the segment, occur in segments 



* This arrangement reminds one of the condition found in JEolosoma, and 

 described in detail by VejdovsL-y in his 'Syst. ii. Morph. d. Oligoch.' p. 101, but in 

 that low form there is no preceding buccal region. 



t Nasse, ' Beit. z. Anat. d. Tubificiden,' 1882. 



