A NEW GENUS OF OLIGOCHiETA. 483 



Gephyrea Chaetiferaj we have the branched " respiratory trees," 

 whose structure appears to show that they are nephridial in 

 nature; even in Sipunculus, two rudimentary diverticula 

 attached to the intestine close to the anus may be homologous 

 structures. It is true that some observers, such as Greef and 

 Spengel, have denied that the anal glands of the Gephyrea are to 

 be compared to nephridia ; but the view of the former was based, 

 partly at least, upon a misunderstanding of these organs. 



There is no regularity that I could detect in the position of 

 the apertures of these tubes ; sometimes two could be observed 

 quite close together, at other times an interval separated two 

 adjacent apertures. One point of importance with regard to 

 the position of the apertures is their limitation to three seg- 

 ments; whether the most anterior of these three segments 

 marks the commencement of the proctodseum or not I am 

 unable to say. Behind the last of the three segments in which 

 they occur the limitations of the individual segments were 

 obscured ; they begin, therefore, in the last properly developed 

 segment. It is well known that earthworms increase in length 

 by the formation of new segments at the posterior end of the 

 body ; it is possible that, as the body increases in length, more 

 of these proctodseal nephridia are developed.^ In fig. 6 is 

 illustrated the greater part of a single nephridial tube ; but it 

 by no means always happens that a tube has so long a course 

 without branching. Very often I have noticed such a tube to 

 divide into two shortly before its opening. 



It has been already mentioned that the nephridia which 

 open into the proctodseum communicate with the general 

 nephridial system only at the septa. As may be seen in suit- 

 able sections, the surfaces of the septa are covered by innu- 

 merable tubes, which anastomose in every direction to form 

 most complicated networks, I have never yet been able to 

 show by a satisfactory preparation the actual form of the net- 

 work in Perichaeta or Acanthodrilus, or in any other 

 form where a network must exist. Spencer (18) has figured 



^ In another specimen I found these nephridia opening into the gut, in the 

 last seven segments at least. 



VOL. XXXI, PAET IV. — NEW SEE. K K 



