76 ALPEED GIBBS BOURNE. 



cephalised region. With regard to the arrangement of valves, 

 in Megascolex (fig. 12) there are valves, as Perrier has de- 

 scribed, in the dorsal vessel between every two segments, and 

 there is also a valve at the junction of each dorso-intestinal 

 vessel with the dorsal vessel. These latter valves consist of a 

 soft-looking tissue which projects as a circular ridge into the 

 dorsal vessel, and in the centre of this is the aperture of the 

 vessel, and M'hen the walls of the dorsal vessel contract tlie 

 efi'ect must be to occlude the apertures of the dorso-intestinal 

 vessels. The dorso-tegumentary vessels present no such valves 

 at their openings into the dorsal vessel, and are placed, more- 

 over, in the anterior portion of eacli segment of the dorsal 

 vessel just posterior to the valve lying in the dorsal vessel 

 itself, so that the effect of a forward peristaltic contraction of 

 the latter must be to force blood into these dorso-tegumentary 

 vessels. 



I cannot help thinking that the arrangement of valves de- 

 scribed by Benham (4, p. 283) for Microchaeta needs con- 

 firmation. His theory that such a valve as he describes at the 

 entrance to each dorso-intestinal vessel serves to direct the 

 blood into that vessel does not seem to me to be based upon 

 sound hydrodynamical principles. 



Two additional sets of facts — the relations of the two sets of 

 intestinal capillaries to one another, and the relations of the 

 intestino-tegumentary vessels — lend support to my view as to 

 the direction of the blood in the branches of the dorsal vessel ; 

 and, moreover, as there is no doubt that in a certain region 

 blood flows from the intestinal capillaries into the supra- 

 intestinal vessel or vessels, and so into the dorsal vessel or 

 into some of the hearts, the opposite view presents this 

 anomaly, that the direction of the blood-flow in the intestinal 

 vessels varies according to it in different regions ; in other 

 words, that some of the dorso-intestinal (or it may be supra- 

 intestino-intestinal) vessels are efferent intestinal vessels and 

 others afferent ; according to my view they are all efferent, 

 and further, the flow of blood always takes place from the 

 dorsal vessel to the various peripheral networks, both in the 



