Editing Development of Darwin's theory (section)

===Homologies in barnacles===
His investigation of barnacles now found how their segmentation related to other crustaceans, showing how they had diverged from their relatives. To Owen, such "homologies" in comparative anatomy showed "archetypes" in the Divine mind, but to Darwin, this was evidence of Descent, showing dramatically how organs could have changed functions to meet new conditions. Darwin was "cock-a-hoop", writing to [[Louis Agassiz]] of this odd metamorphosis and getting him and others around the world to send more barnacle specimens. His cascade of letters made Hooker tire of barnacle details, and write from the [[Himalaya]]s that on reflection he really did prefer to hear the evolutionary speculation after all. Darwin responded that "this is too bad" as "your decided approval of my Barnacle work" had "led me...to defer my species-paper" in the first place.

As his work progressed on to fossil barnacles, pressures brought on illness again and in June 1850 he went to Malvern for a week of treatment. Hooker was helping search for evidence, now trying to test evolutionary ideas and writing that "they have possessed me, without however converting me". While Hooker was not finding gradations of varieties, Darwin's barnacles were showing this to the extent that defining species was extremely difficult.