242 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



dinal vessel is distinguishable anteriorly jnst behind the 

 first seta, and may be traced to. the posterior end of the 

 animal. It receives blood chiefly from branches of the 

 afferent vessels which supply the nephridia and gills. 

 There is in each cheetigerous annnlus a series of connec- 

 tions between these vessels of the body wall, viz., (1) a 

 short transverse vessel on each side connecting the nephri- 

 dia! and dorsal longitudinal vessels, (2) a circular vessel 

 passing across the dorsal middle line, and connecting the 

 right and left dorsal longitudinal vessels, (3) a vessel on 

 each side connecting the nephridial and neural vessels, 

 and (4) a short vessel passing over the nerve cord connect- 

 ing the right and left neural vessels (fig. 24.) The 

 dorsal and nephridial longitudinal vessels supply the body 

 wall in the dorsal and lateral regions, while the neural 

 vessels supply the nerve cord and ventral region of the 

 body wall. All these vessels, which are best seen in 

 transparent young specimens, are indirectly connected 

 by a network of capillaries — the parietal vessels (fig- 

 36). 



The ventral vessel is large and turgid in the greater 

 part of the branchial region, and bears along its course 

 tufts of dark brown filaments (fig. 23). The extent to 

 which these are developed depends upon the size and age 

 of the specimen ; they are much more numerous in old than 

 in young specimens. In old examples the brown filaments 

 are found in other situations also, e.g., along the gonidial 

 vessel of the first nephridium (fig. 27), and upon many of 

 the small vessels situated upon the inner face of the body 

 wall, especially in the branchial region. Each filament 

 (fig. 42) consists of a blindly-ending branch of the blood- 

 vessel on which it is supported, covered with cells which 

 contain large numbers of yellowish or brownish granules 

 which are similar to those found in the chlorogogenous 



