72 ALFRED GIBBS BOURNE. 



vessel immediately posteriorly to the septum which forms the 

 anterior boundary of the segment in which they lie. 



Ventro-tegumentary Vessels (figs. 4, 7 to 9, v. t.). — 

 These are branches of the ventral vessel connecting it with the 

 peripheral network. There is a pair of these vessels in every 

 segment of the body except the first, in which there is a 

 branch of that belonging to the second segment (fig. 8) on 

 each side, and except in those segments in which the ventral 

 vessel is joined by hearts, viz. viii to xiii. 



As mentioned above, the hearts of segments vi and vii do 

 not join the ventral vessel, and in these segments there is, as 

 usual, a pair of ventro-tegumentary vessels. 



In the last segment of the body the ventral vessel simply 

 comes to an end by giving off two of these branches (fig. 11). 



Dorso-intestinal Vessels (figs. 4 to 7, 10, d. i.). — 

 These are branches of the dorsal vessel placing it in connection 

 with the intestinal capillary networks. In segments i to ix 

 there are no such vessels. In segments x to xiii their place 

 is taken by vessels opening into the supra-intestinal vessels, of 

 wl^ich there are two pairs in each segment. These may be 

 called supra-intestino-intestinal vessels. In segments xiv to 

 XVI there is a single pair in each segment, connected, as are the 

 latero-intestinal hearts, with both the dorsal and supra-intestinal 

 vessel (see fig. 5). In segments xvii to cxxxv there are two 

 pairs in each segment, the anterior one being always smaller 

 than the posterior (fig. 10). In segment cxxxvi and the fol- 

 lowing segments to the end of the worm there is only a single 

 pair in each segment, the pair which corresponds to the 

 posterior pair of segments possessing two pairs. 



These dorso-intestinal vessels are usually covered by the 

 yellowish-brown coeloraic epithelium cells which are so con- 

 stantly found in the dorsal region of the alimentary canal. 



The vessels in the segments anterior to the large intestine 

 soon penetrate the intestinal wall ; of those in the region of the 

 large intestine, where there are two to the segment, the ante- 

 rior one always passes round to the ventral region before 

 penetrating the wall, while the posterior one, after having 



