and Anatomy of the Thalassemia and Echiurus, 375 



action of the cilia will remove it through the same channels 

 in a conti'ary direction. 



The vascular system consists of two longitudinal vessels, 

 one running along the ventral surface of the body, the other 

 along the unattached surface of the intestine. The intestinal 

 trunk is always full of blood in the weak or dead animal, the 

 ventral trunk always empty or collapsed. From this circum- 

 stance, from the general arrangement of the vascular system, 

 and from the position of the respiratory organs, we are in- 

 clined to think, although we have not been able to verify the 

 opinion by actual observation, that the former vessel is the 

 venous, the latter the arterial trunk. The vein commences 

 by numerous radicles on the oesophageal portion of the di- 

 gestive tube, runs along the edges of the gut, collecting 

 branches as it proceeds. On the rectum, the trunk disap- 

 pears by being divided into innumerable branches, which are 

 apparently arterial, and proceed to the respiratory sacs, which, 

 as before stated, are highly vascular. The arterial or ventral 

 vessel is apparently formed by radicles from the respiratory 

 sacs (branchial veins). Its walls are thin, and are perceived 

 with difficulty on the surface of the nervous cord. In its 

 course it supplies vessels to the intestines ; and when it arrives 

 at the convolutions of the pharynx, it sends off from its right 

 side a large trunk, which, proceeding to the right oral hook, 

 surrounds it and its muscles by dividing and again closing. 

 It then proceeds to the commencement of the oesophagus, and 

 joins a vessel to be described immediately. The ventral ves- 

 sel, after giving off this great trunk, proceeds to the oral ex- 

 tremity of the pharynx, round which it forms a vascular 

 circle. The latter sends branches back upon the pharynx; 

 and a branch forwards, which forms a second circle or vascu- 

 lar zone round the lip, on the surface of the nervous ring, and 

 a large trunk which, running to the middle of the pharynx, di- 

 lates into a sacculated sinus, which probably owes its peculiar 

 appearance to the transverse contractions into which this por- 

 tion of the tube is generally thrown. This sinus runs along 

 the second portion of the pharynx, and at the commencement 

 of the oesophagus receives the trunk formerly described as 

 proceeding from the ventral vessel. It then terminates by 

 ramifying on the oesophagus, and supplying this portion of the 



