ON TWO NEW GENERA OP AQUATIC OLIGOCH^TA. 277 



In both vessels, particularly in the supra-intestinal, it is easy to see that the blood 

 is a corpusculated fluid ; here and there oval bodies, which have in every respect the 

 appearance of the nuclei in the endothelial lining, may be seen embedded in the 

 coagulated yellow blood. There is little doubt that Lankester's description of 

 corpuscles in the Earthworm's blood will be extended to other, to perhaps all the groups 

 of Oligochseta, in many of which they have been observed by Vejdovsky. 



Here and there the endothelium lining the blood-vessels — particularly at the points 

 where they traverse the intersegmental septa — is thickened to form valve-like structures ; 

 Vejdovsky has described and figured something of the same kind [7] in many other 

 Oligochseta. These agglomerations of cells may be the localities where the blood cor- 

 puscles take their origin through the rapid proliferation of the lining membrane, as 

 Vejdovsky has suggested. On the other hand, the mechanical function of these valve- 

 like structures, which occur in all Oligochseta that I have examined, both terrestrial and 

 aquatic, must not be left out of consideration. The supra-intestinal vessel is connected 

 with the blood-supply of the intestines, and it gives off from the lower side numerous 

 branches which at once break up and form a plexus lying within the oesophageal or intes- 

 tinal walls. The supra-intestinal vessel is also connected in the Xllth segment directly 

 with the ventral vessel. This connection is effected by a pair of great coiled vessels, 

 which I describe later as blood-glands. Further forward the supra-intestinal vessel ap- 

 pears to have no direct connection with the ventral vessel ; there are, however, a number 

 of a perivisceral trunks, thin and coiled, which surround the oesophagus and communicate 

 with the ventral trunk. These take their origin from the dorsal blood-vessel. We thus 

 have in Phreodrilus, as in Lophochceta and Bothrioneuron, a double system of peri- 

 visceral trunks — one set connected with the dorsal and the other with the supra-intestinal 

 vessel. As in Lophochceta there is only one pair of vessels belonging to the latter set. 



The arrangement of the dorsal and supra-intestinal trunks in Phreodrilus is shown 

 in fig. 34 of PL III. The drawing, however, only illustrates a few segments, since I am 

 at present uncertain as to the exact segment where the dorsal vessel terminates pos- 

 teriorly. I have found that in front of the Vlth segment it is the only dorsally placed 

 blood-vessel. In the Vlth segment the supra-intestinal finally disappears, becoming 

 gradually of less and less calibre towards its termination. 



It seems to me, however, to be far from certain that the dorsal vessel of Phreodrilus 

 is the homologue of the dorsal vessel in Tubifex and some of the lower forms. 

 Professor Stolc's important investigations evidently show the need for a more detailed 

 study of the vascular system of Tubifex and other Tubificidse ; it may prove that they 

 are not without the supra-intestinal vessel of Lophochceta and Bothrioneuron. I make 

 this suggestion in entire ignorance of the text of Stolc's paper, which, being in the 

 Bohemian language, is absolutely inaccessible to me. In Pelodrilus, however, a new 

 genus of Phreoryctidse, of which I give some account further on in the present paper, 

 there certainly appears to be no trace of more than one dorsal vessel. 



The question then arises, to which of the two vessels of Phreodrilus does the dorsal vessel 



