144 Transactions. — Zoology. 



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 between the oesopha- 

 geal or intestinal walls. The supra-intestinal vessel is also 

 connected in the twelfth 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 for- 

 ward the supra-intestinal vessel appears to have no connectioii 

 with the ventral vessel ; there are, however, a number of 

 perivisceral trunks, thin and coiled, which surround the oeso- 

 phagus and communicate with the ventral trunk. These take 

 their origin from the dorsal blood-vessel. We thus have in 

 Phreodrilus, as in Lopliochceta and Bothrionenron, a double sys- 

 tem of perivisceral 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. 

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

 vessel of Phreodrilus is the homologue of the dorsal vessel in 

 Tub if ex and some of the lower forms. The question then 

 arises, To which of the two vessels of Phreodrilus does the 

 dorsal vessel of Pelodrilus and other of the lower Oligochceta 

 correspond ? The relations of the single dorsal vessel, which 

 is present in the posterior segments of Phreodrilus, to the 

 intestinal, suggests that it is the equivalent of the single 

 dorsal vessel of other Oligochceta : in this case the vessel 

 which I have termed ' dorsal vessel ' in the anterior seg- 

 ments will be unrepresented in these Oligochceta. There can, 

 I think, be little doubt that the two dorsally-placed blood- 

 vessels of Phreodrilus are the equivalents of the two in Peri- 

 chceta, Acanthodrilus, and a large number of earthworms. In 

 the simpler forms of Oligochceta, then, the dorsal vessel in most 

 cases has disappeared, while the persistent supra-intestinal 

 takes on its functions as well as its own. 



" Testes.— The testes of Phreodrilus lie partly in segment x., 

 but chiefly in segment xi. In longitudinal sections I have 

 found a perfect continuity between the portions of the testes 

 which lie in front of and behind this septum. There is, how- 

 ever, no doubt that in Phreodrilus the germinal tissue is per- 

 fectly continuous through the septum. At both extremities 

 each testis is frayed out into irregularly-shaped processes, 

 which contain the germinal cells in the most advanced stage 

 of development. The body-cavity in the neighbourhood of 

 the gonad is occupied by a quantity of developing and fully- 

 developed spermatozoa. There was no trace of a sperm-sac, 

 which is a nearly universal structure among the Oligochceta. 

 As ripe spermatozoa were abundant in the body-cavity and in 

 the circumatrial sac, I think it probable that no sperm-sac 

 other than the circumatrial space is ever developed. 



