My dear Sir,

I had much pleasure in hearing from you & should have replied more quickly but for the sake of trying to answer your questions less imperfectly.¹

“(1). Do you know of any more conspicuous sexual differences of colour than in our British species.”

No I do not—but North America (as you well know) is the great country for Urodela ² & perhaps some species may exceed our British ones in sexual differences of colour— I have no evidence however that such is the case & the specimens in the British Museum seem to me to afford grounds for believing that the difference is certainly less than in our own Urodeles.

“(2). Has the seasonal dorsal or caudal crest of the male any muscles?”

I have not examined the matter myself but D^r. Günther tells me that not only are there no traces of muscular fibres but that blood vessels & nerves are extremely scanty so that the crest can be cut with very little loss of blood.

D^r G’s observations have, I expect, been made on his Axolotls³

“(3) Is the dorsal or caudal crest a common attribute of the male”

No— I do not know any forms with such a structure except the Axolotl which (as you know is a big, reproductive larva) and Notophthalmus a genus of North American Urodeles so like our own Tritons that I hesitate as to ranking it as a distinct genus.⁴

“(4) are both sexes of any species either permanently or temporarily furnished with a dorsal crest?”

No— The only female that I know of which possesses a crest is the Axolotl. It is much smaller (I am told) than that of the male and then this is a larval form.

“(5) Do males differ from females in external structure in any other way, besides the crest & besides the palmated hinder feet of L. palmipes?”⁵

I cannot call to mind any other external distinguishing character but I have neglected to pay attention to such matters as yet reserving sexual peculiarities, habits &c for the last.

“(6) Do you admit Bell’s genus Lissotriton; or had I better use Triton.?”⁶

I have not made up my mind fully as yet but if I were compelled to decide at once I should decide against “Lissotriton” & speak of Triton punctatus & Triton palmipes.

“(7) Are the males known to fight during breeding season?”

I have never heard or read of any contention for the females though two individuals of Salamandra maculata have been observed to fight—not however for a female.⁷

“(8) Do the males utter any sound, at any time or during the breeding season?”

I know of no sound uttered by foreign Urodeles but no doubt like our own they make a slight noise when tormented   If any English sp is taken (male or female) & its arm, leg or tail be pinched it will probably make a faint “quacking” noise but this applies (as far as I know) equally to males & females as does any development of vocal power set in with the activity of the sexual function.

I am sorry not to be able to answer more completely & satisfactorily. At all times it will afford me much pleasure to reply to any questions you may like to ask as far as I may be able so to do.

I am much interested in the question of “serial homology” a point I touched upon in my paper (in the Trans. Linn. Soc.) on Echidna.⁸

Forgive me if I trouble you with a few words on the matter   I do not wish you to write me a reply but shall hope for a little chat on the subject if you will kindly tell me the first time you are in town & at liberty or better still, if you will give me again the priviledge of seeing you at my cottage.⁹

Having been much struck with the resemblances & differences between the pectoral & pelvic limbs in Man & Apes—I turned to the Echidna hoping to find in that relic of the past facts calculated to elucidate the [old] relations— I did not find so many as I expected & I turned to the Reptiles & worked at the myology of Iguana   The result has certainly not been more satisfactory.¹⁰

I am now working at the muscles of the Urodela   Surely these Amphibia may be expected to shew traces of the earlier conditions of vertebrate limbs— would you not think so?— The tarsal & Carpal structures of these creatures correspond in a wonderful manner as Gegenbaur has shewn—¹¹ In the Chelonia the limb bones of the pectoral & pelvic limbs resemble each other wonderfully   the Chelonia have relations with the Anourous Amphibia but could the former be supposed to be nearer the common starting point than the latter are?¹²

Some Lemurs (eg Loris Nycticebus) present resemblances between the muscles of the pectoral & pelvic limbs greater than those existing in mammalian forms higher or lower in the scale¹³   Can it be that there is some law of correlation developing a resemblance between pectoral & pelvic limbs in forms which have descended from others in which the differences between those parts were greater & their resemblances less?

I know that double thumbs sometimes coexist with double great toes but have you ever heard of similar deformities or pathological conditions developing themselves in other homotypical parts of the pectoral & pelvic limbs? eg. Ilium—scapula knee joint—elbow wrist—tarsus &c

I have read with great interest your account of the tendency of the foot of pigeons to develop a sort of wing(!) & your references in your recent work Vol. II. p. 322 to the observations of Isid Geoffroy & Meckel.¹⁴

Your admirable work I have just read through once with great pleasure & much profit, I am just about to read it through again.

I feel sure you will kindly forgive me for troubling you so much about “limbs” & that you will also afford me an opportunity of talking with you a little on the subject at some convenient season.

Believe me | My dear Sir | Your’s very truly | S^t George Mivart

C. Darwin Esq.