rostellum

the rostellum of the stigma of violets, or of the operculum of many mosses

The rostellum has an outer firm pouch, inside which is the viscid substance to which are firmly attached the caudicles of the pollinia. An insect entering the fl. probes the spur of the labellum and its back comes into contact with the rostellum and depresses the pouch, causing the viscid substance to adhere to the insect.

The morphology of the scolex, particularly the rostellum, is also useful in diagnosis; T. saginata has no rostellum and its scolex bears no hooks, making it easily distinguishable from T. solium, which has an armed rostellum.