KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 15. N:0 7. 31 



Concerning the distribution of the above species elsewhere I am entirely ignorant, 

 as I have not succeeded in identifying them with any previously known. It is true that 

 several species from Russia have been described, which are likely to be identified with the 

 Siberian, but as of the former we at present know hardly any thing more than the 

 length, the colour of their body, the number of segments etc, i. e. merely external cha- 

 racters, I hope to be excused if I do not even attempt to identify them. 



Regarding- the distribution of the species in the countries with which we now 

 occupy ourselves, a few remarks will present themselves. 



All in all Novaja Semlia seems to be the richer in species, compared with the 

 vicinity of the Jenissej, or any one of the other countries visited by the expeditions. 

 Of the 20 species described 10 are found in the island of Novaja Semlia, 1 in Green- 

 land, 1 on Jalmal, and 8 about the river Jenissej. 



With regard to endemic species we find that: Novaja Semlia has 8, Norway 2, 

 Greenland 1, Jalmal 1 and Jenissej 6 or rather 5, as one of them is found in the south 

 of Siberia between the towns Tomsk and Krasnojarsk. 



Of all the 20 species only 2: M. primcevus and N. callosus are common for both 

 Novaja Semlia and Jenissej, and only 1 : A. tenéllus is found both in Norway and in 

 Siberia about the Jenissej, but in the former country this species is represented only 

 by a distinct variety. 



Again, with regard to the genera, Mesenchy trams has 1 endemic species in Novaja 

 Semlia, 1 at the Jenissej, and one common to both localities. Arcliienchytrceus has 4 en- 

 demic species in Novaja Semlia, 1 in Greenland, and 5 at the Jenissej or in Siberia, 

 none occurring in both places. And of the 7 species of Neoenchytrams 3 are endemic in 

 Novaja Semlia, 1 in Jalmal, 2 in Norway, none on the Jenissej, but 1 is found ranging 

 över the whole territory from Novaja Semlia and nearly to the headwaters of the Jenissej. 



After these short remarks on our present knowledge of the distribution of the 

 aretie species of EnchytraBus, I may perhaps now pass över to a comparison between 

 their principal organs and their evolution, as far as can be judged from their unequal 

 development in the different species. I begin with 



the nervöns system. 



The front part of the nervous system or the supra-oesophagial ganglion exhibits 

 in the different species a great variety of form, and in fact almost every species may 

 be more or less characterized by the shape of that organ, so as to be sufficiently 

 distinguished from allied forms, and alivays from forms of different genera. 



The histologi cal strueture, on the other hand, is less variable, and nearly always 

 the same, even in different genera. 



The concavity and convexity of the posterior margin of the supra-oesophagial 

 ganglion has formerly been considered as the character of species only, and it seemed to 

 be quite sufficient as such, as long as a few species only were known to exist. Leydig, I 



