Dr. W. Michaelsen on the Enchytrgeida3, 419 



Claparfede's. In order to decide upon this point I have sub- 

 jected Eisen's genera to a thorough revision, in which it was 

 no small advantage to me that I was able personally to inves- 

 tigate most of the species worked at by Eisen, and to com- 

 pare them with the Enchytrgeidee of our fauna. I take this 

 opportunity of offering my best thanks to M. Gustav Eisen 

 and to Prof. Sven Loven, by whose kind intervention I was 

 enabled to make these investigations upon the valuable arctic 

 materials. 



I arrived at the following result. Eisen's chief principle 

 of classification, the more or less advanced fusion of the two 

 halves of the cerebrum, when applied in too one-sided a 

 fashion, leads to the establishment of unnatural genera. As 

 such I must characterize the genera Arcliiencliytrceus and 

 Neoencliytrceus^ which are separated from each other only by 

 the form of the cerebrum. As evidence of the insufficiency of 

 this principle of classification I may cite tlie two species of 

 the genus Buchholzia^ which will be treated in detail further 

 on ; their near relationship must strike every one who com- 

 pares them. But according to the form of the cerebrum B. 

 appendiculata, Buchh., must be referred to Mesencliytrceus, 

 while B.fallax, aut., possesses the cerebrum of an Archten- 

 chytrcBus. It would, however, be wrong to deny that the 

 form of the cerebrum is of essential importance in some respects. 

 In the second line we must assign it a certain significance in 

 many Enchytrseid-groups. Thus the two known species of 

 the perfectly natural genus Anachceta, Vejd., possess an 

 almost exactly similar Neoenchytrceus-cexebmm. In those 

 EncJiytrcei also which group themselves around E. hegemorij 

 Vejd.*, and which are distinguished by the constant presence 

 of dorsal pores, by the unequal length of the setae in the same 

 tuft, and by the occurrence of lateral sacs on the receptaculum 

 semi'ms, the Neoenchytrceus-cei'ehrum predominates. {E. lohi- 

 fer^ Vejd., alone, according to that author, possesses a poste- 

 riorly emarginate cerebrum f.) 



Further, those Pachy drill of which we know the form of 

 the cerebrum, with the exception of P. fossor^ Vejd. [loc. cit. 

 pi. xiii. fig. 9), possess a cerebrum deeply emarginate at the 

 posterior margin. Lastly, I might in this place cite a fourth 

 natural group of Enchytr^idas in which a definite form of 

 cerebrum is characteristic ; but it first of all needs to be 



* E. Tiegemon, E. galha, E, Leydigii, E. lohvfer, E. Penieri, Vejd., aud 

 E. tenuis, aut. 



t (7) Vejdovsky, " Beitr. z. vergl. Morphol. d. Aunelideu : I. Mono- 

 gvaphie der Euchytrttiden " (Prague, 1879), pi. ix. fig. 3. 



