42 



OLIGOCHAETA 



The naked eye characters of the excretory system of this kind are very obvious ; 

 the absence of the large paired tubes cannot be passed over, and the delicate ramifying 

 tubes especially attached to the septa can hardly be missed, at any rate in well- 

 preserved specimens ; very often these tubes are massed into the semblance of paired 

 nephridia, three or more pairs to a segment ; this is often seen among the Acantho- 

 drilidae ; in the Perichaetidae, on the other hand, the network is more diffuse and 



not broken up into separate masses. In Mega- 

 wolicles and also in Megascolex armatus the diffuse 

 network of minute tubules is reinforced by the 

 existence of larger paired tubes, one pair to each 

 segment. These large paired nephridia appear to 

 be in connexion with the smaller tubes. 



In Octockaetus there seems to be no connexion 

 from segment to segment of the nephridia, though 

 the nephridial mass of, at any rate, each side of 

 each segment forms a perfectly continuous net- 

 work ; there are no funnels in the anterior region 

 of the body, and the external pores are not so 

 numerous as they are in Perichaeta. In the 

 hinder region of the body the nephridia are also, 

 as will be described more at length presently, 

 connected with the gut ; and the excretory system 

 of this part of the body differs from that of the 

 more anterior segments in two points : in the 

 first place there are funnels, and in the second 

 place there is no question at all about a network 

 which is most clear ; I have figured this network 

 (53), which often becomes so close that the inter- 

 spaces are mere trabeculae of limited extent, 

 traversing a kind of excretory sinus ; the net- 

 work in the anterior part of the body has 

 rather to be inferred ; I have never actually seen 

 a branching of the tubules, but as the orifices 

 to the exterior are numerous, and as there is 

 nowhere any break of continuity, a network must exist ; in any case there is no 

 doubt whatever about its existence, in the hinder end of the body. The tubes which 

 lead to the exterior often branch in the thickness of the body-wall, and often run 



MEGASCOLIDES. 



(After Spencer.) 



A portion of execretory system of two segments. 

 i. Nephridial tube in body-wall. 2. Funnel. 

 3. Septum. 4-6. Nephridial tubes cut in various 

 directions. 7. External pores. 



