These directories contain the result of the Ubuntu automated merge system, fondly known as the Merge-o-Matic or just "mom". Merges are generated by combining both the Ubuntu and Debian changes since their first common ancestor and leaving any conflicts to be resolved by human hand.
The layout is the same as a Debian FTP pool, so to see the merge for debhelper see the d/debhelper directory and to see the merge for libraw1394 see the libr/libraw1394 directory. In each directory you will find a REPORT file that tells you what the files mean and what to do.
To grab all the relevant files for a merge, a grab-merge.sh script is available. Be sure to run it from a scratch directory as any other contents will be lost.
Status pages showing the outstanding merges for each component are available, choose main, restricted, universe or multiverse.
For some merges, Merge-o-Matic cannot determine the base version for the merge, and you have to perform the merge by hand. These are listed for main, restricted, universe and multiverse.