There is a tree with branches depicting a postulation on how related genera would be formed, main text reads:
Case must be that one generation then should be as many living as now. To do this & to have many species in same genus (as is) requires extinction.
"Thus between A & B immense gap of relation. C & B the finest gradation, B & D rather greater distinction. Thus genera would be formed. — bearing relation
But the most evocative part is the small note in the upper left:
Darwin's notebooks are available online through Darwin-online.org.uk. You can open a notebook and browse the pages as though flipping through them in person.
In early June, the New York Times published a story on the Open Tree of Life Project, the goal of which is to draw "a tree of life that includes every known species. A tree, in other words, with about two million branches."
[Source: New York Times, June 5, 2012 "Open Tree of Life Project ]