Dr. W. Michaelsen on the Enchytr£eida3. 427 



drilus side by side with the genus Enchytrceus, and then 

 divides the latter, in accordance with Eisen's principle of 

 division, into the three subgenera MesenchytrceuSj Archienchy- 

 trceus, and Neoenchytrceus. (He, however, retains for the 

 different species the name of the principal genus Enchytrceus.) 

 Against this combination we have the circumstance that the 

 true Mesenchytrmi (at that time only Eisen's three species), 

 as being Enchytrgeidee without salivary glands, and with sig- 

 moidally curved setse, cannot be arranged under the genus 

 Enchytrceus ; they come much nearer to the PachydriU. As, 

 further, the fourth species which Vej do vsky has placed in this 

 subgenus, namely Enchytrceus [Buchholzia, aut.) appendicu- 

 latuSj Buchh., in my opinion is to be separated from the genus 

 Enchytrceus, Vejdovsky's subgenus of the species of Enchy- 

 trceus with the cerebrum straightly truncated behind must 

 altogether fall. I might, certainly, have divided the genus 

 Enchytrceus of my system into the subgenera ^r(;A^e^^c^^/<rcB^^s 

 and Neoenchytrceus, but I do not think that this would have 

 produced a natural grouping. The genus Enchytrceus for the 

 present remains a collective genus. 1 have not yet thoroughly 

 worked through the species of this genus, and I am therefore 

 still without the insight necessary to enable me at present to 

 state by what principles of division their breaking up into 

 natural groups may best be effected. I believe, however, that 

 by the changes which I have made in the classification, I 

 have made a step in the right direction, on the road which 

 will lead us to a satisfactory, natural classification of the 

 interesting family of the Enchytrseidge. 



EXPLANATION OF PLATE XVIII. 



Fiy. 1. Mesenchytrceus Beumeri, aut. a. Bundle of setae, h. Lympli- 

 corpuscles. c. Cerebrum, seen from above ; c, commissure ; k.n, 

 cephalic nerve ; om, upper, urn, lower pair of cerebral muscles. 

 d. Segmental organ, e. Transverse section of the dorsal -s essel 

 with the cardiac body. /. Seminal sac. 



Fig. 2. Mesenchytrceus Jlavidus, aut. a. Seminal sac. b. Cerebrum 

 (references as in fig. Ic). c. Segmental organ, d. Seminal 

 duct. 



Fig. 3. Mesenchytroius minibilis, Eisen. a. Tangential section through a 

 lobe of the segmental organ, b. Transverse section through the 

 dorsal vessel, with the cardiac body. 



Fig. 4:. BuchholziafaUa.r, ant. a. Bundle of setse. 5. Lymph-corpuscles. 

 c. Transverse section through the cesophagus, with the diverti- 

 culum (corresponding to the author's figure {&), tig. 8). d. Cere- 

 brum (references as in fig. 1 c). e. Seminal sac. 



m' 



