A flow pipe which serves also for expansion is taken from the top of the cylinder to a point above the cold - water supply and turned down to prevent the ingress of dirt.
The application of vestibules is practically limited to trains making long journeys, as it is an obstruction to the free ingress and egress of passengers on local trains that make frequent stops.
For three months during each year business was suspended, and all ingress or egress except for the most necessary purposes was forbidden.
To remedy these defects vestibules were introduced, to enclose the platform with a housing so arranged as to be continuous when the cars are made up into trains, and fitted with side doors for ingress and egress when the trains are standing.
It is characteristic of the group that the mouth should be the only means of ingress to and egress from the digestive sac and that no true perivisceral space or coelom exists in the sense in which these terms are used in higher Invertebrates.