330 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



some time these contractions become less violent, as the 

 animal becomes exhausted, until, finally, all movement 

 ceases except the occasional contraction of the intestine. 

 The body of the worm becomes somewhat flattened, and 

 the chloragogen cells, which at first completely hide the 

 underlying tissues, become clearer. It is-ihen possible to 

 investigate the blood vessels which pass to the intestine 

 wall. These branches become filled with blood, and, if 

 the worm is lying on its side, are comparatively easy to 

 see. The number and arrangement of these smaller 

 intestinal vessels vary in different parts of the body. The 

 largest vessel, which has already been described, is 

 constant. The variable ones are the accessory intestinal 

 branches which lie between the intestinal proper and the 

 perivisceral trunk (PI. VI, fig. 42). In the anterior 

 segments of the intestinal region of the body there may be 

 as many as five pairs of accessory intestinal vessels, all 

 branched and forming a vascular network over the 

 intestinal wall, but they do not appear to have any 

 connection with the ventral vessel. In the posterior 

 segments these vessels gradually decrease in size and 

 number, and become very difficult to follow. 



(o) The Perivisceral Vessels are present in all 

 segments of the body except segment 8. They arise 

 in pairs from the dorsal vessel near the posterior border of 

 each segment, and are connected with the ventral vessel 

 below. These are quite large trunks, passing out almost 

 at right angles to the dorsal vessel, and form in most 

 segments a series of complex coils, often extending from 

 one end of the segment to the other (PI. VI, fig. 42, 

 pv. v.). This coiling of the perivisceral vessels allows of 

 ample freedom of motion for the worm — a very necessary 

 precaution in view of its rapid and sudden movements. 

 They do not branch, and, therefore, there is no integu- 



