I am truly obliged for all the trouble which you have taken for me, and for your very interesting note. I had only vaguely heard it said that frogs had a rudiment of a sixth toe; had I known that such great men had looked to the point I should not have dreamed of looking myself. The rudiment sent to you was from a full-grown frog; so that if these bones are the two cuneiforms they must, I should think, be considered to be in a rudimentary condition. This afternoon my gardener brought in some tadpoles with the hind-legs alone developed, and I looked at the rudiment. At this age it certainly looks extremely like a digit, for the extremity is enlarged like that of the adjoining real toe, and the transverse articulation seems similar. I am sorry that the case is doubtful, for if these batrachians had six toes, I certainly think it would have thrown light on the truly extraordinary strength of inheritance in polydactylism in so many animals, and especially on the power of regeneration in amputated supernumerary digits. (178/1. In the first edition of "Variation under Domestication" the view here given is upheld, but in the second edition (Volume I., page 459) Darwin withdrew his belief that the development of supernumerary digits in man is "a case of reversion to a lowly-organised progenitor provided with more than five digits." See Letters 161, 270.) LETTER 179. TO J.D. HOOKER. Down [October 22nd, 1864]. The Lyells have been here, and were extremely pleasant, but I saw them only occasionally for ten minutes, and when they went I had an awful day [of illness]; but I am now slowly getting up to my former standard. I shall soon be confined to a living grave, and a fearful evil it is. I suppose you have read Tyndall. (179/1. Probably Tyndall "On the Conformation of the Alps" ("Phil. Mag." 1864, page 255).) I have now come round again to Ramsay's view, (179/2. "Phil. Mag." 1864, page 293.) for the third or fourth time; but Lyell says when I read his discussion in the "Elements," I shall recant for the fifth time. (179/3. This refers to a discussion on the "Connection of the predominance of Lakes with Glacial Action" ("Elements," Edition VI., pages 168-74). Lyell adheres to the views expressed in the "Antiquity of Man" (1863) against Ramsay's theory of the origin of lake basins by ice action.) What a capital writer Tyndall is! In your last note you ask what the Bardfield oxlip is. It is P. elatior of Jacq., which certainly looks, when growing, to common eyes different from the common oxlip. I will fight you to the death that as primrose and cowslip are different in appearance (not to mention odour, habitat and range), and as I can now show that, when they cross, the intermediate offspring are sterile like ordinary hybrids, they must be called as good species as a man and a gorilla.