A Syrian refugee boy is seen shortly after arriving at a beach in a raft overcrowded with migrants and refugees in the Greek island of Lesbos

A Syrian refugee boy is seen shortly after arriving at a beach in a raft overcrowded with migrants and refugees in the Greek island of Lesbos, November 20, 2015. Balkan countries have begun filtering the flow of migrants to Europe, granting passage to those fleeing conflict in the Middle East and Afghanistan but turning back others from Africa and Asia, the United Nations and Reuters witnesses said on Thursday. REUTERS/Yannis Behrakis