ON MONOPYLEPHORUS LIMOSUS. 21 



found on the dorsal side of the lateral neural canals. The lateral 

 bundles are very fine and consists each of only one or two fibres 

 running along the lateral border of the fibrillar portion of the cord. 

 In a word the musculature of the nerve cord of this species is of 

 the type found most commonly in tubificid oligochsetes. 



6. Vascular system. 



The vascular system consists of the dorsal vessel, the ventral 

 vessel, the intestinal and the integumentary networks. 



1). The dorsal vessel runs through the whole length of the 

 body, lie for the greater part on the right side of the intestine 

 and has a thick coating of chloragogue cells. It commences at 

 the beginning of the first segment in the dorsal median line near 

 the body wall. Running backwards directly under the brain the 

 vessel passes through its posterior notch and again comes to lie 

 very near the dorsal body wall. It then turns slightly toward the 

 alimentary canal and lies between the median pharyngeal glands 

 in segment III. In segment IV it lies close to the dorsal median 

 fine of the intestine. The vessel swells more or less suddenly in 

 segment V and forms the longitudinal pulsatory heart which ex- 

 tends from thence backwards halfway into segment XI, running 

 mostly on the right side of the intestine. Behind the longitudinal 

 heart the dorsal vessel runs also along the right side of the intestine 

 to near the hind end of the body, where it regains its original 

 median position. The dorsal vessel gradually becomes thicker 

 posteriorly from the front end of the longitudinal heart, and in the 

 greater part of the middle of the body its width is mostly one 

 eighth that of the body ; but more posteriorly it becomes again finer. 

 From about one-third, of the body length backwards the dorsal 

 vessel runs apart from the intestine and is provided with a chlora- 

 gogue coating of its own. 



