From A. C. L. G. Günther   19 December 1867

British Museum

19.12.67.

My dear Sir

Many thanks for your photograph.1

The keeper in the Zoolog. Gardens is quite right with regard to the difference in color in the sexes of Rattlesnakes.2 This case is perfectly analogous to that of the common viper, which I mentioned to you the other day. I do not know of any sexual structural (external) difference in snakes, except that the tail of males is generally longer & more slender.

Male snakes are always smaller, & generally more brightly coloured, & with the markings more distinctly defined than females.3

As regards other Reptiles, I will mention some remarkable cases in Indian species, & thinking that you are a subscriber to the Ray Society, & have at hand my book on Indian Reptiles, I may refer you to the pages.4 If you have not the book, let me know it, & I will supply you with further details.

Page 130 & 131. Pl. 13. figs F & G. Ceratophora stoddartii & aspera. The rostral appendage is perfectly analogous to the comb of a cock, being but little developed in the female & young.5

Page 132. Cophotis   The dorsal crest is much more developed in the male than in the female.6 This is one of numerous similar instances, all of which show that in Lizards with a dorsal crest, this is more developed in the male. Iguana is such an example.

p. 135. pl. 14. fig. A. Sitana is a lizard with a very large gular pouch, entirely absent in the female. There are other Lizards in which both sexes are equally provided with a gular pouch.7

p. 143 | Calotes nigrilabris offers a remarkable instance of sexual difference in coloration of the head & body.8

Sexual differences in coloration of snakes I have mentioned particularly in Tragops dispar p. 304, Dipsas cynodon p. 308, Trimeresurus erythrurus p. 386.9

As regards Frogs, the case of Megalophrys montana p. 413–414 is very striking; the male has a rostral appendage (skinny), absent in the female; it has a pointed appendage above the eye, much less developed in the female; & some tubercles on the back, also absent in the female.10

So much for today. If I come across other cases, I shall note them. I think, to appreciate fully the instances mentioned, you ought to look at the specimens when you come to the Museum.11

Many thanks for the promised book, on Variation; you underrate me when you say, that it will contain very little which can interest me.12

Yours sincerely | A Günther

CD annotations

1.1 Many … females. 3.2] crossed ink
2.4 except … slender. 2.5] double scored blue crayon
3.1 Male … females. 3.2] scored blue crayon
4.1 As … body. 8.2] crossed pencil
5.1 Page … example. 6.4] ‘Reptiles’ added above blue crayon
6.1 Cophotis] ‘ceylanica’ added pencil
6.2 This … male. 6.3] scored red crayon; ‘White band plainer— the stripes more [clearly] defined’ added pencil13
7.1 p. 135.] ‘3’ added at top of page, blue crayon, circled blue crayon
8.1 p. 143 … body. 8.2] ‘very variable in above | see Cophotis’ added pencil
9.1 Sexual … p. 304, 9.2] scored blue crayon; ‘Snakes’ added blue crayon
9.1 Sexual … p. 386. 9.2] crossed ink
9.2 dispar] ‘Tragops’ added pencil; ‘4’ added at top of page, blue crayon, circled blue crayon
10.1 As … me. 12.2] crossed pencil; ‘Batrachia’ added above blue crayon
3
CD and Günther probably met during CD’s visit to London from 28 November until 7 December 1867 (CD’s ‘Journal’ (Correspondence vol. 15, Appendix II)). CD cited Günther on the sexual differences of snakes in Descent 2: 29–32.
4
Günther refers to Günther 1864; there is an annotated copy in the Darwin Library–CUL (see Marginalia 1: 352).
5
In his copy of Günther 1864, CD marked passages on the pages indicated by Günther (see Marginalia 1: 352). In Ceratophora stoddartii (the rhino-horned lizard) and C. aspera (the rough-horned lizard), pronounced appendages develop on the heads of males alone (Günther 1864, pp. 130–1; Descent 2: 34). Figures F and F’ of plate 13 in Günther 1864 were reproduced in Descent 2: 34 to indicate the difference between male and female C. stoddartii.
6
The reference is to Cophotis ceylanica (the pygmy lizard; see Günther 1864, p. 132, and Descent 2: 32).
7
Figure A of plate 14 in Günther 1864 shows the expanded gular pouch of the male Sitana minor (the fan-throat lizard; now S. ponticeriana) and is reproduced in Descent 2: 33.
8
See Günther 1864, p. 143. CD noted the different coloration of body and lips in Calotes nigrilabris (the black-cheek lizard) in Descent 2: 36. See also plate facing p. 151.
9
CD included brief information on sexual differences in Dipsas cynodon (the dog-toothed cat snake; now Boiga cynodon) and Tragops dispar (Gunther’s vine snake; now Ahaetulla dispar) in Descent 2: 29–30.
10
CD cited this information from Günther 1864 in Descent 2: 26. Megalophrys montana (the horned frog) is now Megophrys montana.
11
Günther refers to the British Museum.
13
The dorsal scales, and the white band between mouth and shoulder, are more distinct in males of Cophotis ceylanica (Günther 1864, p. 132). CD quoted Günther on this subject in Descent 2: 32, 36.

Please cite as “DCP-LETT-5733,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-5733