THE NEPHRIDIUM OF LUMBRICUS. 309 



although the cells are of very great size and relatively few in 

 number^ whereas in Microchaeta they are small but very 

 numerous : in fact, we have perhaps a stage in the transition 

 between perforated cells and a more definite epithelium. 



3. Comparison with other Genera. 



Although we have, in numerous recent contributions, outline 

 figures of the complete nephridium with the funnel of various 

 Oligochseta, yet we have very few details as to the histological 

 structure of the diff'erent parts of the tube. 



Amongst the majority of the Microdrili (in the ^Mimi- 

 colous" Oligochsetes) there appears to be no distinction 

 of the nephridial tube into more than two regions : for example, 

 amongst the Enchytrseidse (see Michaelsen's and Vejdovsky's 

 works) we find (a) the post-septal portion consists of a more 

 or less extensively convoluted " narrow tube '^ embedded in 

 a mass of vesicular cells ;^ and {h) a praeseptal portion, con- 

 sisting of the simply constructed funnel and a short ciliated 

 tube leading to the post-septal tube (see PL XXIV, fig. 27). 



In Tubifex, however, where the coils of the nephridium are 

 free, Vejdovsky (32) figures (a) a narrow region, {b) a middle 

 or glandular region, and (c) a terminal or wide region, in addi- 

 tion to (c?) the praeseptal region. As in Lumbricus, the tube 

 is surrounded by vesicular cells (see also Kukenthal, 24). 



In the literature of the earthworms or Macrodrili, also, the 

 detailed information as to the character of the tube of the 

 nephridium is very scanty. Beddard (6) describes the different 

 calibres of the tube in Perichaeta aspergillum and P. 

 arm at a, where three regions are evidently present, cor- 

 responding to the *' narrow," '' middle ciliated," and " wide " 

 tubes; the last has striations in its wall. In Ac. multi- 

 porus a similar variation in calibre is noted (loc. cit., fig. 14), 

 but only two regions are apparently distinguishable. Beddard 



1 Michaelsen, in his description ofPachydrilus sphagnetorum ('Arch, 

 f. Mikr. Anat.,' xxxi, p. 491), states the whole of the tube is ciliated ; and iu 

 Enchytrseus Mobii and others, he figures this tube as slightly dilated jus<", 

 before the external aperture. 



