316 OLIGOCHAETA 



Zellsubstanz fast auf das Minimum reducirt ist.' The part of the nephridium which 

 lies in front of the septum is little more than the funnel. As regards the lobate 

 character of the post-septal part of the nephridium, attention may be here directed 

 to Eisen's figure (13, PI. xiv. fig. 38) of the nephridium of Neoenchytraeus hyalinus, 

 a species put by Michaelsen into the genus Enchytraeus, as restricted by him. 

 It would appear from this figure that the species should be referred to the genus 

 Mesenchytraeus. Another peculiarity of the genus, though restricted to two species, 

 M. arviatus, M. setosus, is the existence of specially enlarged setae in certain segments 

 of the body; these are referred to under the description of the species where they 

 occur. The reproductive organs are remarkable in that there are, as in most 

 Oligoehaeta, though not in other Enchytraeidae, sperm-sacs and egg-sacs ; the 

 sperm-sacs are paired, the egg-sac is usually single ; the varying length of these 

 sacs may be useful as a specific character, but it seems more probable that the 

 length varies according to age and degree of maturity. The spermathecae open at 

 one end into the gut ; they may or may not be provided with diverticula ; when 

 these are present they vary in number. 



(i) Mesenchytraeus primaevus, Eisen. 



Mesenchytraeus primaevus, Eisen, Ofv. Svensk. Akad. 1878, No. 3, p. 68. 

 Eneh3rtraeus primaevus, Vejdovskt, Syst. u. Morph. 1884, p. 41. 

 Enchytraeus (Mesenchytraeus) primaevus, Vaillant, Annel^s, p. 269. 

 Definition. Length, 10 mm. ; breadth, i\mm.; setae, 5-8 per bundle; number of segments, 

 52. Spermathecae, very small, trilobed at free end; sperm^duct hardly longer than 

 funnel. Hob. — Nova Zembla ; Siberia. 



Eisen distinguishes this species principally by the excessive minuteness of the 

 spermathecae, which are said to be ' at least ten times smaller ' than those of other 

 species. Eisen considers that this is not due to the immaturity of the organs though 

 he confesses that no spermatozoa were found in them. The cardiac body is thick in 

 cross section with irregular swellings, and composed of numerous cells. 



(3) Mesenchytraeus mirabilis, Eisen. 



Mesench3d;raeus mirabilis, Eisen, Ofv. Svensk. Akad. 1878, No. 3, p. 68. 

 Enchytraeus mirabilis, Vejdovsky, Syst. u. Morph. 1884, p. 41. 

 Enchytraeus (Mesenchytraeus) mirabilis, Vaillant, Anneles, p. 268. 



Definition. Length, 10-15 w«.; breadth, \\-%mm.; number of segments, 64; setae, 5-7 



