225 
weie gieasy. If some material is spread in a flat glass-cup and 
water is poured over it, the Mononchs wili mount rapidly and be 
lying on the surface dry and shilling. This peculiarity I have only 
observed in one genus besides the Mononchs, namely in the genus 
bonus. It seems to be a peculiarity of these genera; I have seen 
it as well in Ironus ignavus as in Ironus longicaudatus and it is 
the case with all the species of Mononchus I have exainined. It 
is very remarkable and it has surprised me that it is mentioned 
nowhere in the literature. In the case referred to, the Nematodes 
suddenly swarmed to the surface of the water which was poured 
out over the material in a glass cup: they resembled perfectly 
diminutive steel-needles which had suddenly become alive, and it 
was now an easy matter — on account on the largeness of the 
species — to pick them up and place them into a watch-glass. 
The examination of the animals gave the following result: 
the females reached the length of 4 mm, the males the length of 
3,6 mm. As to form and aspect the animals agree in some measure 
with the Mononchus papillatus. Behind the head the body is 
inconspicuously constricted. The cavity of the mouth is about 
twice as long as wide, the distal half being a little wider than the 
proximal half in that this is tapering towards the oesophagus, in 
the distal end of which it is ending pointed. In this way 7 the 
oesophagus is encompassing about the proximal third of the mouth- 
cavity. The dorsal tooth is placed in the upper half of the mouth 
and its apex is running obliquely inwards and forwards. The de- 
current edge of the tooth is visible to the commencement of the 
oesophagus. Opposite to the tooth is found a thickened chitinous 
ridge the middle of which is serrated. Between this and the tooth 
another chitinous list is seen without serration and relatively incon- 
spicuous. The shape of the cavity of the mouth is on account of 
these lists prismatic, triangular in transverse section. The oeso¬ 
phagus is verv muscular and has a conspicuous chitionous intima, 
which reaches a little way downwards into the lumen of the intes- 
tine, a case not uncommon in the Mononchs. The vulva is placed 
Vidensk. Meddel, fra den naturli. Foren. 1911. Bd. 63. i k 
