“— 
4 Nils Hj. Odhner. 
genera have been established each on one species, and two 
new species and a new variety have been described and assigned 
to genera previously known, but not hitherto recorded from these 
regions. Thus the number of Norwegian Solenogastres has been 
increased to comprise 13 species. 
Owing to the scantity of the material, difficulties have arisen 
in its thorough examination, which has therefore to be based, in 
most cases, on only one or two specimens. To some extent, how- 
ever, these drawbacks could be obviated owing to the fact that 
these animals have a symmetrical organization; this circumstance 
made it possible to study the anatomy by cleaving the object 
longitudinally and using one of the halves for dissection under a 
binocular microscope, and the other, if necessary, for cutting in 
transverse sections. By the combination of these methods a satis- 
factory knowledge of the entire organization was gained. Only 
in one or two cases was it possible to obtain a complete series 
of sections, transverse as well as longitudinal, the material being 
exceptionally large enough to be utilised for this purpose. 
Two facts concerning the Norwegian Solenogastres are rather 
remarkable: namely (1) that the group in this region is much 
differentiated in various directions so that each species, as a rule, 
constitutes a genus of its own, and (2) that so many of the 
genera (up to 7) are common to the Northern Pacific region 
whence Heatn, in his excellent monograph (1911), has described 
a number of new forms and genera apparently limited to the 
said area. These facts may to some extent be due to the insuffi- 
cient exploration of the northern and arctic regions with respect 
to the Solenogastres, but certainly also other factors have in- 
fluenced the phenomenon. The cause of the said peculiarities may 
perhaps be revealed by the assumption that the Solenogastres are 
a very ancient group of animals which during a considerable 
lapse of time has become highly specialized but which in prere- 
moe eras was widely distributed. An expansion in recent times 
of these deep-water forms from a region so remote from the other 
does not appear to be supported by the facts known as to the 
possibility of migration in the latest geological epochs. 
That the Solenogastres, in all probability, are a primitive 
group of animals and must even be distinguished from the Mol- 
lusca is an opinion which has strongly borne out by the in- > 
vestigation of the present material. The reasons on which this — 
