The graphic indicates a chain of handlers.
In the graphic, an arrow leads from a system labeled Sender to an envelope that has a Header part in it besides other parts. This envelope is labeled SOAP Message. An arrow leads from this envelope to a block labeled Message Handler. The block contains a pair of wheels in its top-left corner. This Message Handler block spreads out to indicate that there is a chain of Message Handler blocks. An arrow leads from this Message Handler chain to another system that is labeled Receiver.