422 Dr. W. Micliaelsen on the EnchytrEeidse. 



rior inversions (spermatozoa-sacs and ovisacs) are formed by 

 the dissepiments xi./xii. (for the spermatozoa) and Xil./xiii. 

 (for the ova). M. B eumeri jyossesses two spermatozoa-sacs, 

 which extend, to the rig-ht and left of the intestine, as far as 

 the posterior wall of segment Xil. In M. mirahilis I found 

 only one, which, however, perforates the following dissepi- 

 ments, and extends into segment xxvi. Within the seg- 

 ments it is dilated ; the dissepiments produce narrow constric- 

 tions upon it. A median ovisac stretches below the intestine 

 in M.flavidus into segment xvil., in M. Beumeri and M. 

 falciformis into segment XIX., and in M. mirahilis even into 

 XXIX. The length of the sac may, however, be different in 

 different individuals of the species. I have given the extremes 

 noted by me. In M. mirahilis the ovisac also shows dilata- 

 tions and constrictions. In M. Beumeri and M. jiavidus it is 

 of uniform thickness throughout. The function of oviducts 

 is performed by two symmetrical funnel-shaped inversions of 

 the dissepiment xil./xiii., which open outwards by trans- 

 verse slits in the ventral line of setas^ in front of the tufts of 

 setse of segment xiii. As probably in all Enchytrgeidge, with 

 the exception of the genus AnachcBta, ^^jd., the seminal 

 ducts in the Mesenchytrcei are united and communicate with 

 the intestine. This I have been able to ascertain positively 

 in M. falciformis, M. Beumeri, and M. flavidus. 



From all this it appears clearly enough that the genus 

 MesencJiytrceus, Eisen, is a natural one. As a second point, 

 therefore, I find that it must be received into the system. 

 Although the name Mesenchytrceus was chosen only in. oppo- 

 sition to Archienchytroius and NeoenchytrceuSj I will never- 

 theless retain it without adopting the latter, as the genus 

 Mesenchytrceus of Eisen's classification exactly coincides with 

 this genus as defined by me. 



I have detected two species in the German region, namely 

 M. Beumeri and M. flavidus. 



Mesenchytroius Beumeri, aut. (4). 

 Pachydriliis {Me!ienchytr(sus) Beumeri, aut. (4). 



I have elsewhere given an accurate description of this 

 worm (4, pp. 44-46). I therefore confine myself to eluci- 

 dating what was there stated with figures (PI. XVIII. fig. 1) . 



As localities I can cite the marshes of the Elbestrand 

 below Flottbeck, near Hamburg, the Borstler Beck on the 

 Baxtehud road behind Harburg, and the Eppendorier Moor, 

 near Hamburg. It lives chiefly under moss and bark on 

 rotten black tree-stumps. 



