420 Dr. W. Michaelsen on the Enchytr^idee. 



proved that the group is a natural one. T refer here to the 

 genus MesenchytrceuSy Eisen, which occupies a special position 

 in Eisen^'s system, inasmuch as it is not founded, like the other 

 two, solely upon the form of the cerebrum. In what follows 

 I indicate the results of my comparative investigations upon 

 Eisen's and the German Mesencliytrcei. To this I shall 

 append a description of the genus Buchliolzia, so as then to 

 pass to the establishment of a system of the Enchytreeidee 

 such as, in my opinion, gives the best expression to the rela- 

 tionships existing in this family. 



Genus Mesenchyte^us, Eisen (2) . 



Enchytra>Ms (Mesenchytrceus) , Vejd.* 

 Pachydrilus {Mesencliytrceus), aut. (4). 



The MesenchytrcBi are Enchytrseidse with strongly sig- 

 moidally-curved setee (PI. XVIII. fig. 1, a), without dorsal 

 pores or salivary glands. They possess a large, distinctly 

 recognizable cephalic pore, which is situated at the apex of the 

 head-lobe or close to it, as has been described by me in M. 

 Beumeri (4, p. 19, and 6, fig. 14). In this way they are essen- 

 tially distinguished from the Pachydrili^ in which the cephalic 

 pore is small, and placed in the dorsal median line between the 

 head- lobe and the cephalic ring. Eisen unfortunately has 

 stated nothing about head-pores ; but by means of serial sec- 

 tions I have been able to make out with certainty that in this 

 respect M. 'primcevus and M. falciformis exactly agree with 

 M. Beumeri. Of three specimens of M. mirahilis which were 

 at my disposal, the cephalic extremity had unfortunately been 

 cut away behind the zone in two of them, while the third 

 showed a slight injury to the head-lobe. Nevertheless I 

 believe that in this last specimen I recognized a cephalic pore 

 near the anterior margin of the head-lobe, but I cannot assert 

 positively that I was not deceived by an artificial production. 

 The Mesenchytrcei (judging from our native species) possess 

 colourless blood and a cardiac body, like that of many Poly- 

 chasta, such as Terehellides Strdmii and Pectinaria helgica \. 

 Firmly attached to the inside of the wall of the vessel in 

 the ventral median line, this traverses the whole of the dorsal 

 vessel. It consists of cells of various sizes with distinct cell- 

 walls and nuclei and a fine protoplasmic granulation. In M. 



* (8) Vejdovsky, 'System, und Morphol. der Oligocliseten,' Prague, 

 1884. 



t (9) Michaelsen, " Ueber Chylusgefasssystein bei Euchytraeiden/' in 

 Arch, fiir mikr. Anat. Band xxviii. (Bonn, 1886), p. 301, figs. 10 and 11. 



