— 
Norwegian Solenogastres. 51 
the animal the fold originates as a papilla projecting from the 
bottom of the ciliated crypt (fig. 79). From the outset the fold is 
rather broad and contains beneath the ciliated epithelium glandular 
cells and some fine fibres (cf. Simrothiella). Further rearwards the 
fold diminishes in size, and from the margins surrounding it a 
lateral fold begins to differentiate. These folds are distinct along 
the greater part of the ventral furrow and consist of elongated 
epidermis and glandular cells, but differ from the median fold in 
having both their sides (except the base of the inner one, within 
the furrow) covered with cuticular plates like the epidermis in 
general. Towards the hindmost end the lateral folds are obliterated 
again, and adjoin the margins of the furrow, and lastly the median 
fold also joins them, rising as a small papilla from the under side 
of the body (fig. 80) rather far in front of the comparatively narrow 
cloacal opening. No invaginated pit appears between the latter and 
the fold end. 
Beneath the cuticula, on a transverse section, there is obser- 
vable a thin muscular layer of circular fibres and beneath them 
there are scattered oblique, and within them longitudinal, ones. The 
latter are most frequent on the under side of the body, but they do 
not unite into strings at the sides of the ventral furrow but are 
spread over the whole under side (figs. 83, 84). In the feeble devel- 
opment of the peripheric muscles, Gymnomenia represents a pri- 
Mitive stage relatively to other Solenogastres. The septal muscles, 
on the other hand, are much more powerfully developed than the 
longitudinal ones, they too, however, are spread in the dissepi- 
ments and not united to fascicles as for instance, in Drepanomenia. 
At the bottom of the ventral furrow they enter the circular muscle layer. 
The septal muscles are stronger in the hind part of the 
animal than further anteriorly. The direction of the septal muscles 
is somewhat different from that observed in other Solenogastres e. 
g. Drepanomenia. Whereas in this species they radiate from a 
common root at each side of the ventral furrow, they have in 
Gymnomenia a somewhat transverse course. Some fibres radiate 
from the strong basal parts of the cords which issue at the sides 
of the ventral furrow, but others are inserted more laterally and 
have a dorsal extension, so that, indeed, they cross the radiatiag 
ones (fig. 84). As for the latter, they are fixed at the body wall lower 
than the dorso-ventral ones, and their undermost cords extend to 
the latero-ventral corners of the body. These median fibres, 
