STRUCTURE OF EARTHWORM ALLIED TO NEMERTODRILUS. 559 



them, probably ensures less injury through pressure. These 

 tubes, like the rest, appeared to be entirely empty, or, at any 

 rate, to be filled with an absolutely clear fluid ; they give ofiF 

 numerous branches on all sides ; the commencement of the 

 branches, which run along the segments from end to end — that is, 

 in a longitudinal direction — could be seen in transverse sections 

 as elliptical foramina in the walls of the tube (see fig. 14). The 

 branches which pass downwards ramify among the longitudinal 

 muscles, and even on the dorsal side of the body of the worm. 

 Where there are no conspicuous longitudinally-running trunks 

 the branches reach the thick layer of connective tissue which 

 lies to the inside of the longitudinal muscles ; arrived there, 

 they pass in different directions, longitudinal as well as trans- 

 verse. Besides the main transverse trunks running between 

 the two muscular coats I observed vessels of less calibre, run- 

 ning, as shown in the diagram (fig. 16, a), just below the peri- 

 toneum, and apparently continuous right round the body. 



The branches which pass upwards could be traced as far as 

 the epidermis ; they were constantly, like the other branches, 

 accompanied by blood-capillaries. I could not detect the 

 actual orifices, but at frequent intervals the non-glandular cells 

 of the epidermis were closely crowded together. At these 

 points I imagine lie the external orifices which are so evident 

 upon the cuticle when it is stripped off and examined. 



In no case were cilia observable along the course of the 

 tube. It is clear that this system of tubes forming a plexus 

 within the muscular coats or the body-walls is a new form of 

 excretory organ, and unlike any that has been hitherto described 

 in any Oligochsete. 



A plexus of nephridial tubes, not interrupted by the septa, 

 occurs in a good many forms ; but it has been hitherto found 

 to lie in the coelom, or is at most partly retro- peritoneal ; 

 besides, in the genera (Perichseta, Megascolides, &c.) 

 which have excretory organs of that pattern the tubes are to 

 some extent ciliated; in those forms there are numerous 

 external pores, and so the integument is perforated by numerous 

 nephridial tubes. These may even branch on their way to the 



