560 PRANK E. BEDDARD. 



§ Circulatory System and Perihsemal Spaces. 



The principal account of the circulatory system in this family 

 of Oligochseta — and that is very incomplete — is contained in 

 a paper upon Eudrilus by myself (15). The blood-vessels 

 of Libyodrilus are very similar, but I did not find a sub- 

 nervian trunk. Very frequently in transverse sections a blood- 

 vessel could be seen lying beneath the peritoneal membrane, 

 and vertically beneath the nerve-cord ; but by following out 

 the vessel through a few sections it was invariably found to be 

 merely a part of the integumental blood plexus running for a 

 short distance in a longitudinal direction. The dorsal vessel 

 is united with the ventral by a series of paired " hearts." 

 These increase in size posteriorly. The dorsal vessel is 

 ensheathed by a layer of ^' chloragogen " cells, beneath which 

 is a thin layer of very delicate muscular fibrils ; the aper- 

 tures of the hearts into the dorsal vessel are guarded by 

 valves consisting of a mass of granular columnar cells with 

 small nuclei ; there are similar valves where the hearts 

 debouch into the ventral vessel. The supra-intestinal 

 trunk is recognisable only in the oesophageal region of the 

 worm ; it is very easily seen in dissections, and its calibre 

 is quite equal to that of the dorsal vessel. The supra-intestinal 

 differs from the dorsal blood-vessel in having only a very thin 

 peritoneal layer ; there are no large chloragogen cells like the 

 pear-shaped cells which cover the dorsal vessel, only a cover- 

 ing of much flattened cells : the supra-intestinal trunk is 

 united with the dorsal by a vertical sheet of mesentery. The 

 supra-intestinal vessel is directly concerned with the blood 

 supply of the oesophagus. As already mentioned, the oesophageal 

 walls contain an extremely rich meshwork of blood capillaries ; 

 in specimens that happen to have been killed with this part 

 of the vascular system naturally injected, the walls are rendered 

 turgid by the contained capillaries, which have almost the 

 appearance of forming a continuous sinus ; here and there the 

 supra-intestinal vessel is connected with this network by a 

 short tube. 



The presence of infra-oesophageal vessels has been 



