In the Book Professional JMS from Wrox, I have some questions regarding concurency in the Example : JMS with EJB 1.1

My first I thought about the Asynchronous message receiving with MessageLister was that it would be multi-threaded. Meaning that a thread would be created for each incoming Message from the Queue and that the function ‘onMessage’ would run concurrently. I found out this is not the case and each Message is processed one after the other (I did the test with openJms).

In the Wrox example, the MessageListener forwards each JMS message to a Stateless Session Bean. If 50 Messages arrives in the Queue, there will be no concurrent processing at all. Is there something I am missing here?
This is not even close to what Message Driven Bean can achieve.