I doubt whether any insects can be shown with any probability to have been flower feeders before the middle of the Secondary period. Several of the asserted cases have broken down. Your long letter has stirred many pleasant memories of long past days, when we had many a discussion and many a good fight. LETTER 399. TO J.D. HOOKER. Down, August 21st, 1881. I cannot aid you much, or at all. I should think that no one could have thought on the modification of species without thinking of representative species. But I feel sure that no discussion of any importance had been published on this subject before the "Origin," for if I had known of it I should assuredly have alluded to it in the "Origin," as I wished to gain support from all quarters. I did not then know of Von Buch's view (alluded to in my Historical Introduction in all the later editions). Von Buch published his "Isles Canaries" in 1836, and he here briefly argues that plants spread over a continent and vary, and the varieties in time come to be species. He also argues that closely allied species have been thus formed in the SEPARATE valleys of the Canary Islands, but not on the upper and open parts. I could lend you Von Buch's book, if you like. I have just consulted the passage. I have not Baer's papers; but, as far as I remember, the subject is not fully discussed by him. I quite agree about Wallace's position on the ocean and continent question. To return to geographical distribution: As far as I know, no one ever discussed the meaning of the relation between representative species before I did, and, as I suppose, Wallace did in his paper before the Linnean Society. Von Buch's is the nearest approach to such discussion known to me. LETTER 400. TO W.D. CRICK. (400/1. The following letters are interesting not only for their own sake, but because they tell the history of the last of Mr. Darwin's publications--his letter to "Nature" on the "Dispersal of Freshwater Bivalves," April 6th, 1882.) Down, February 21st, 1882. Your fact is an interesting one, and I am very much obliged to you for communicating it to me. You speak a little doubtfully about the name of the shell, and it would be indispensable to have this ascertained with certainty. Do you know any good conchologist in Northampton who could name it? If so I should be obliged if you would inform me of the result. Also the length and breadth of the shell, and how much of leg (which leg?) of the Dytiscus [a large water-beetle] has been caught. If you cannot get the shell named I could take it to the British Museum when I next go to London; but this probably will not occur for about six weeks, and you may object to lend the specimen for so long a time. I am inclined to think that the case would be worth communicating to "Nature." P.S.--I suppose that the animal in the shell must have been alive when the Dytiscus was captured, otherwise the adductor muscle of the shell would have relaxed and the shell dropped off.