278 MR FRANK E. BEDDARD 



of Pelodrihts and other of the lower Oligochseta correspond ? The relations of the single 

 dorsal vessel, which is present in the posterior segments of Phreodrilus, to the intestinal, 

 su^ests that it is the equivalent of the single dorsal vessel of other Oligochseta ; in 

 this case the vessel which I have termed " dorsal vessel " in the anterior segments will 

 be unrepresented in these Oligochseta. There can, I think, be little doubt that the two 

 dorsally placed blood-vessels of Phreodrilus are the equivalents of the two in Perichceta, 

 Acanthodrilus, and a large number of Earthworms. In the simpler forms of Oligochseta, 

 then, the dorsal vessel in most cases has disappeared, while the persistent supra-intestinal 

 takes on its functions as well as its own. 



§ Blood-Glands. 



Many of the Lumbriculidse are provided with peculiar csecal diverticula of the dorsal 

 vessel. These have been recently compared by Grobben to the "pericardial glands" 

 of the Mollusca. I have myself described in Perichceta a series of "blood-glands" 

 formed by a network of capillaries, with frequent dilatations crowded with corpuscles 

 and surrounded by a layer of chloragogen cells, which appeared to me to be referable 

 to the same category. In Phreodrilus there is a structure which is more plainly of a 

 glandular nature than the vascular appendices of the Lumbriculidse or the blood-gland of 

 Perichceta. In the Xllth and Xlllth segments is a wide, irregularly coiled tube of which 

 a portion is illustrated in fig. 34, b.gl. I cannot be certain of its exact shape, as the 

 bending and twisting was so complicated that I have hesitated to attempt a re-construc- 

 tion from my sections ; this tube exists on both sides of the gut, and appears to 

 connect the supra-intestinal and ventral blood-vessels. It is the morphological equivalent, 

 I believe, of the perienteric vascular loop of its segment. But it evidently has a quite 

 different function. 



The vessel in question has the comparatively thick muscular coat of the dorsal blood- 

 vessel. Its interior is almost entirely solid, but here and there were conspicuous blood- 

 clots, about the nature of which there could be no doubt ; these clots are coloured pink in 

 my figure (PL I. fig. 6, hi.). 



The solid mass, which occupies the greater portion of the lumen of the tube, is 

 made up of cells. The arrangement of these cells seems to indicate that they are simply 

 the lining of the vessel which has, for the most part, become so thick as to occlude 

 the lumen, or nearly so. The cells are large and vesicular ; they are almost unstained, 

 only the nucleus having been acted upon after a fairly long immersion in borax 

 carmine ; the cells contain a number of granules. They resemble most nearly the tall 

 cells which form the valvular structures in the blood-vessels of the Oligochseta, and like 

 them are probably to be looked upon as a local proliferation of the lining membrane of 

 the vessel. I am not aware whether there is any special development of the lining 

 epithelium of the lateral appendages of the dorsal vessel in Lumbriculus ; but I am 

 inclined to believe that the two structures correspond very closely. The immensely 

 larger size of the blood-gland in Phreodrilus than in the Lumbriculidae is, perhaps, 



