78 ALFRED GIBBS BOURNE. 



We must now consider the intestino-tegumentarj' vessels^ 

 and we shall find that the conclusion we have just arrived at 

 simplifies matters enormously with regard to these vessels. 

 There has hitherto existed considerable uncertainty as to the 

 direction taken by the blood in these vessels. Perrier (9, pp. 

 496, &c.)j after an admirable discussion of the subject^ in 

 which he was evidently tempted, on account of the connection 

 between the capillaries at the anterior extremities of the only 

 pair of these vessels known to him and those at the anterior 

 extremity of the dorsal vessel, to believe that there was in the 

 vessels in question a backward flow, a conclusion to which he 

 afterwards came for Pontodrilus, states that the blood flows 

 forwards in them, in Urochseta. If, as I have asserted on in- 

 dependent grounds, the blood flows forwards in the portion of 

 the ventral vessel anterior to the hearts, all difficulty disap- 

 pears, the blood flows from the dorso-tegumentary and ventro- 

 tegumentary vessels into peripheral networks, and from these 

 iuto the intestino-tegumentary vessels, and from these again 

 into the intestinal capillary networks. So that the afi'erent 

 vessels of these latter are the intestino-tegumentary vessels, 

 which accords with the theory that I have advocated above 

 that the dorso-intestinal vessels are their eff'erent vessels. 

 These arrangements obtain not merely with respect to the 

 large anterior pair of intestino-tegumentary vessels of the 

 cephalised region, but also with respect to those which occur 

 in every other segment of the body. Yet one more point with 

 regard to the subject of the preceding paragraphs. According 

 to previous theories the blood at the anterior region in such 

 a worm as Megascolex either flows forwards in three trunks 

 and backwards in one, or backwards in three trunks and for- 

 ward in one; if what I have said is true, the blood flows 

 forwards in two trunks and backwards in the other two, 

 which, as all four trunks are of approximately the same calibre 

 when filled, seems a more probable arrangement. 



Further, a reference to the various memoirs will show what 

 doubt there has always been as to any special peripharyngeal 

 vessel, i. e. pair of commissural vessels uniting the dorsal and 



