My dear Huxley

I called twice in Jermyn St. but unfortunately found you once lecturing & secondly out.—² It is by no means the carpal or tarsal bones which are increased in number, but generally only the digits & metacarpals.³ Indeed until the whole hand becomes doubled or bifurcated, it appears that the carpal bones are not increased. This same doubling puzzles me; but yet, I think, the wonderfully strong inheritance & thrice repeated growth shows that there is something in the case.⁴ May I say that the digits, (divided by many joints in the rays) are indefinite in number & very generally more than five in the pectoral fins of Fishes? How are Sharks &c in this respect? These being one of oldest orders would be best.—⁵

Now there is one other point, for which I sh^d. be very glad of information & bears on a remark made by you: I am told that Roget (no good authority) says in Bridgewater Treatise that in Frogs or Toads there is a rudiment of a sixth digit.⁶ Have you any specimen in spirits? I think I remember a tubercle behind. If there is one, could you spare time to dissect this tubercle & see whether in bone or other respect there is any reason to suppose that this really is rudiment of 6^th digit. I have heard vaguely of two cases of six-toed frogs on hinder limb. If it should turn out a rudiment, you will, I know, allow me to quote you.

Ever yours | C. Darwin

Do not forget, whenever you can screw out time— rudiment of 6^th toe on [front] or Hind foot of Batrachian.—