Scenario: A node sends an ip packet through several hops on a large ip network (the internet) to make a request from a web server for the first time. I know the packet contains, among other things, headers of the assigned ip/mac address of this sender intended to be used as a return address by the server.

Question: Are the ip/mac return addresses that the web server eventually recieves those of the originating node, or are they the ip/mac of the first router in the line of return hops to that node?
In otherwords, in the process of multiplexing and demultiplexing the headers through the stack of each consecutive router, are the ip/mac headers replaced with that of the next, successive router, all the way up to the web server (ergo the server only has to wory about sending the return packet to the first router in the return line), or is the ip/mac info of the original sender preserved as it hits the web server?