CD is not surprised at CC’s entire rejection of his views. Agrees that there is no direct proof of unlimited variation. Says natural selection should be viewed as comparable to wave theory of light: it is probable because it groups and explains a host of facts in several fields of science.

Agrees Louis Agassiz’s review [Am. J. Sci. 2d ser. 30 (1860): 142–55] is not unfair, but Agassiz misunderstands CD. His "categories of thought" are to CD merely empty words.

Regrets that his health prevents their meeting, but offers some suggestions for the expedition to the Malay Archipelago and coast of China: the search of caverns in the Malay Archipelago for fossil bones, deep sea dredging in the tropics, glacial action in any moderately steep mountains, means of geographical distribution, the history of domestic animals in these regions, and gestures and expressions of real savages as compared with our civilised expressions. [See 5008 and 5011.]