KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 15. N:0 7. 33 



nated anterior margin and a nearly straight posterior one. In one specimen of M. prim- 

 cevus the posterior margin had a small but very deep circular emargination, but I sup- 

 pose it to be an abnormal one, as I clid not observe it in other specimens. The 

 cerebral ganglion of said species is the least differentiated one of all, and the two halves 

 are separated by a deep oblong groove running parallel to the longitudinal diameter 

 of the body. 



The various species of Neoenchytrasus are also differently developed, but 

 showing all a strong tendency to centralisation of their principal organs. The 

 least developed species is N. fenestratus, its supra-oesophagial ganglion being but 

 slightly convex. The simplicity of its receptacle indicates also its low phylogenetic 

 standing. The same ganglion is concave in front. In the three allied forms: JSf. Stux- 

 bergi, Vejdovski and hyalinus the cerebral ganglion is more elongated and its posterior 

 margin still more convex, but the anterior margin of said ganglion is, as in former spe- 

 cies, concave. In N. callosus, durus and Ratzeli both margins of the cerebral ganglion 

 are convex, indicating a higher differentiation of the original two lobes, as we found 

 them in M. primwvus. Neoenchytrseus is therefore naturally divided into two groups: 

 one with a convex posterior margin, and the other where both the anterior and poste- 

 rior margins are convex. The latter group may be considered the most developed, 

 which is also verified by the development of its other organs. As the highest developed 

 species of this genus I consider Neo. Ratzeli, both on account of its cerebral ganglion 

 and its receptacle. 



An infra-oesophagial ganglion does not exactly exist, and Ratzel has properly 

 remarked that Enchytraus is the only genus which is wanting in ganglionic congrega- 

 tions at the anterior end of the ventral nervetrunk. In many species however there 

 exists a strong ganglionic swelling at said place, the trunk being somewhat prolonged 

 and also emitting a long slender nerve towards the lower lip of the mouth. This 

 nerve is well developed in M. falciformis, in many or perhaps in all species of Archi- 

 enchytrceus, in N. Stuxbergi, but does not exist, or at least is not observed, in the 

 otherwise highly developed N. durus and callosus. 



The segmentation of the ventral nervetrunk is more or less developed. In some 

 or perhaps in most of the species the swelling in each segment is hardly perceptible, 

 in others (Neoenchytr. Stuxbergi and Vejdovskyi) on the contrary very large and con- 

 spicuous, and in the former species also a small side nerve is found in the fourth seg- 

 ment, which is the only case where it occurs in this family. 



In Archienchytrams nervosus the ganglionic sAvellings of the 4 th and the 11" 1 and 

 12 th segments attain an enormous development, and surpass the supra-cesophagial gang- 

 lion several times in size. 



It is remarkable that said swellings are found only in the segments containing 

 the organs of generation. In A. profugus and nasutus I have sometimes found certain 

 irregular nervous enlargements in some of the segments, but not to be compared in 

 size with those above. 



K. Sv. Vet. Alcad. Handl. Bd. 15. N:o 7. "-' 



