To Frederick Smith   4 April [1860]¹

My dear Sir

I am much obliged for your note.— Whenever you have finally determined about the Bee, not that it is likely that you will find cause to change your opinion, I will carefully measure the diameter of the cells; & if, as I fully believe, they are sensibly larger, the fact will be curious. The more curious, as Reaumur thought the size so fixed, that he proposed this as a universal standard of measurements for mankind!²

Thanks for information about the genera allied to Pompilus, which I did not know.— I had heard of Calathus & wish I knew where I could obtain more special information,—viz whether all the gradations in size of wing occur in the same place, or whether the variations are local, &c &c.—

With sincere thanks for your never-failing kindness, believe me | My dear Sir | Yours sincerely | C. Darwin

P.S Waterhouse wants much to see the gradation between common & Drone cells.—³