172 W. B. BENHAM. 



gas or fluid will be more rapid where this exists than where it 

 is replaced by a network. 



(b) With regard to the longitudinal tegumentary vessels 

 arising from the dorsal and ventral vessels in Somite xiv, the 

 only earthworm presenting an arrangement at all like that in 

 Sparganophilus is Criodrilus lacuum. Rosa describes 

 and figures (fig. 4, '' Sul Cr. lac./^ in 'Mem. d. R. Acad. d. 

 Sci./ Torino, xxxviii, 2nd ser.) a single longitudinal branch 

 on each side arising from the commissural vessel connecting 

 dorsal and subneural vessels in Somite xii, and running for- 

 wards on the body-wall beyond Somite vii. These " vasi 

 ricorrenti " are applied against the body-wall, along the lateral 

 line, and send no branches to the intestine. 



Longitudinal vessels, at first sight similar to those in Crio- 

 drilus and the present worm, are met with in Urochseta, 

 Megascolex, Microchseta, Lumbricus, and others, where 

 they have received the name " intestino-tegumentary.'^ But 

 in reality these are very different, for they are in relation 

 chiefly with the gut wall, from the plexus in which, in the 

 majority of cases, they arise, though in Lumbricus the two 

 vessels are branches from the dorsal vessel in Somite x. As 

 Bourne! j^^s shown, tliese longitudinally placed vessels corre- 

 spond with short vessels occurring in each somite behind xiii, 

 which terminate at each end in a capillary plexus, at one end 

 on body-wall, at the other on gut wall. The intestino-tegu- 

 mentary vessels likewise arise from network on gut-wall, and 

 send branches to body-wall. 



The " intestino-tegumentary " vessels, too, lie in close 

 apposition to the oesophageal wall, whereas the tegumentary 

 vessels of Criodrilus and Sparganophilus adhere to the 

 body-wall and have no connection with gut-wall. But just as 

 the intestino-tegumentary vessels are modified representatives 

 of the posterior raetamerically arranged short vessels, so it 

 would appear that the tegumentary vessels are very elongated 

 representatives of branches to the body-wall, given off by 



' "On Meffascolex cocrulcus," ' Quart. Journ. Micr. Sci.,' vol. xxxii. 



