68 ALFRED GIBBS BOTJRNE. 



neural, described by Perrier (9) as occurring in segments 

 VIII, X, and xiii, in Urochseta, may be special commissural 

 networks. 



Another capillary network, which, if it exists in any worm, 

 would be a commissural network, is that connecting the dorsal 

 and ventral vessels at their posterior extremities. From 

 observations which I have made upon Megascolex, as well as 

 upon some small worms, mounted alive in a compressorium, I 

 believe that there is no such special network, but that the 

 terminal branches of these vessels behave just like any other 

 of their branches (fig. 11). Jaquet (6), however, speaking of 

 Lumbricus, says that the dorsal and ventral vessels " se 

 mettent en relation par des anastomoses reciproques " at their 

 posterior extremities. 



Peripheral Networks. — I would give this name to all 

 the capillary networks in the skin in which the blood under- 

 goes aeration, also those in the septa — in fact, all those which 

 do not belong to the intestinal system ; and I think we are 

 justified in grouping all these together, as they all have 

 similar relations with the large vessels, and are all meta- 

 merically arranged. 



In Megascolex, at any rate, these always establish communis 

 cation between the dorsal, ventral, and intestino-tegumentary 

 vessels. They lie for the most part in the superficial region 

 of the body- wall, but they are also to be found in all the 

 various tissues and viscera, excepting only the alimentary 

 canal, and even here the exception does not extend to the 

 pharyngeal and gizzard region. I have not had sufficient 

 material to work out their exact arrangement in the nerve- 

 cord, nephridia, generative organs, or walls of the large blood- 

 vessels, in which latter they are to be found as vasa vasorum, 

 but I am satisfied that in all these cases they have relations 

 similar to those of the networks found in the body-wall. I 

 believe that in all cases branches of the dorsal, ventral, and 

 intestino-tegumentary vessels enter into connection with them. 

 They are certainly continuous across the dorsal median line, 

 and I believe also from segment to segment, though not of 



