It is made by dusting on a specially prepared adhesive surface finely powdered fibres of cotton or silk.
The epithelial layer consists of (1) so-called " indifferent " cells secreting the perisarc or cuticle and modified to form glandular cells in places; for example, the adhesive cells in the foot.
Other genera are Aglauropsis, Gossea and Gonionemus; the last named bears adhesive suckers on the tentacles.
In some species of Rana and Staurois inhabiting mountainous districts in south-eastern Asia, the larvae are adapted for life in torrents, being provided with a circular adhesive disk on the ventral surface behind the mouth, by means of which they are able to anchor themselves to stones.
The wheels are coupled, but the feature of the engine is that the couplingrods act merely to keep the high-pressure and low-pressure engines in phase with one another, very little demand being made upon them to transmit force except when one of the wheels begins to slip. In this arrangement the whole of the adhesive weight of the engine is used in the best possible manner, and the driving of the train is practically equally divided between two axles.