— 218 — 
fail in ascertaining on the spot where the hind clinging- 
organ had just let loose the presence of a silk-lock. In this 
way it was practically proved that the clinging-organs are 
anchored exclusively in a silk-lock spun previously by the 
larva on to the substratum. 
Moreover I was able to render visible also to the naked 
eye on a tray on which some living larvae had been creeping 
about for some time the numerous silk-locks which said 
larvae whilst creeping about had fixed to the bottom and 
to the vertical sides of the dish, by colouring these silk-locks 
with ordinary writing-ink. 
The invagination of the hind clinging-organ during the 
process of letting loose could also be clearly observed. 
I noticed how during the invagination and the loosening of 
the hind clinging-organ the rectal-gills were entirely drawn 
in to be stuck out again immediately after the re-anchoring 
of the hind clinging-organ, the ensuing releasing of the front 
clinging-organ and the stretching of the body. 
I furthermore observed how by fixing alternately the 
front and the hind clinging-organ the larvae can also move 
against a very strong current. (cf. the schematical figure 
on page 210). 
Neither in May 1917 nor in May 1918 did I find any 
Simulium-pupae in the D Hevrane. In August 1918 however 
I found a great number of these pupae there. 
