Sends some questions on secondary sexual differences of fishes [missing], which he hopes AG will look over.
Invites AG to come to Down.
Encloses queries on sexual differences and nest-building habits of fish.
Down.| Bromley.| Kent. S.E.
My dear D
You were so kind as to say that I might ask you some
questions.— I have roughly written out my short discussion
about secondary sexual differences of fishes, chiefly from your
information; & some points have occurred to me about which I
Be so, kind as to give enclosed note to M
When I saw you in London, you said that you would run down here. We shall be most happy to see you at anytime, & you can come down on the Saturday evening or Sunday morning, whichever suits you best, & sleep here & in all probability I can send you in some vehicle as early as you like on Monday morning to the Station.— Bromley is 6 miles distant; but Orpington, (a new station on S. E. Railway) is only about 3 miles distant, though more distant from London.—
With most sincere thanks for all the very great kindness which you have shown towards me, pray believe me | Yours very sincerely | C. Darwin
(1) Am I right in supposing that the two sexes of Callionymus are described by Yarrell as C. Lyra (the male) and C. dracunculus as the female? Yarrell says nothing about the first dorsal fin being brightly striped in C. Lyra which, if I am not mistaken, you said was the case.
(2) Am I right in believing that both sexes of some species of Blennius have a crest, & that neither sex is thus furnished in B. pholis?
(3) Yarrell speaks in a manner which makes me suppose that perhaps both sexes of some Gasterostei are crimson beneath. Is this the case? I see that neither sex is crimson beneath in some species.
(4) Are the sexes known to differ in Colour in any other species of Labrus, besides L. mixtus?
(5) Cuvier says that some species of Gobius make nests; now do any of these species differ at all sexually in colour?
(6) Do any of those fishes which deposit their eggs within the mouth or within the marsupial sac of the male differ sexually in colour?
(7) are Crenilabrus massa and melops, which build nests, brightly coloured species; or is it known that they become brighter during the breeding season?
(8) Do any other genera besides crenilabrus, gobius & gasterosteus build nests.
(9) M. Carbonnier maintains that the females of all fishes grow to a larger size than the males. Is there any truth in this? You told me of some Cyprinodontae in which this is the case. Do you believe that the females of many kinds of fish are larger than the males? Or do you know of any cases in which the males are larger than the females?
- f1 7186.f1The year is established by the relationship between this letter and the letter from A. C. L. G. Günther, 13 May 1868.
- f2 7186.f2For CD's discussion of secondary sexual characters in fish, see Descent 2: 1--23. Günther had sent CD information on Cyprinodont fish in his letter of [late December 1867 or early January 1868] (Correspondence vol. 15). The two men had probably also met at the British Museum in London in March: see letter to A. C. L. G. Günther, 23 March , n. 2.
- f3 7186.f3See enclosure, and letter from A. C. L. G. Günther, 13 May 1868.
- f4 7186.f4The note has not been found. George Henry Ford, an artist at the British Museum, provided the illustrations for chapter 12 of Descent, on fish, amphibians, and reptiles.
- f5 7186.f5Günther apparently did not visit Down until 22 to 24 January 1870 (Emma Darwin's diary (DAR 242)). Orpington was on the Chislehurst to Sevenoaks extension of the South Eastern Railway; the branch opened on 3 March 1868 (Cox 1988, p. 48).
- f6 7186.f6CD refers to William Yarrell and his History of British fishes (Yarrell 1836, 1: 261--8). Yarrell mentioned the suspicion that Callionymus lyra (the gemmeous dragonet) and C. dracunculus (the sordid dragonet) were male and female of the same species in ibid., p. 266--7. Callionymus dracunculus is now a `suppressed' name, synonymous with C. lyra (Pauly 2004, p. 59). For Günther's discussion of C. lyra, its misclassification as two species, and its appearance, see Günther 1859--70, 3: 139--41. CD gave a reference to this discussion in a note dated 21 June 1867 (DAR 82: B5). See also Descent 2: 7--9.
- f7 7186.f7For crested and uncrested blennies, including Blennius pholis, see Yarrell 1836, 1: 223--38. Yarrell makes no distinction between male and female blennies. CD remarked that in some species of blenny, only the male was crested, and in some, both sexes were crested, in a note dated 21 June 1867 (DAR 82: B5--6). Blennius pholis is a synonym of Lipophrys pholis.
- f8 7186.f8Gasterosteus is a stickleback genus. Yarrell in Yarrell 1836, 1: 81, comments of the first three species he lists (Gasterosteus trachurus, G. semiarmatus, and G. leiurus), `Some exhibit various shades of crimson and purple; but these colours are more frequent in males than females'. These three names are all synonyms of G. aculeatus. Yarrell also describes G. pungitius (now Pungitius pungitius) and G. spinachia (now Spinachia spinachia) as having no red coloration (Yarrell 1836, 1: 85--9).
- f9 7186.f9CD described the coloration of Labrus mixtus, the red wrasse, in Descent 2: 9. Günther had shown him specimens in June 1867 (see DAR 82: B6, note dated 21 June 1867).
- f10 7186.f10CD refers to Georges Cuvier and Cuvier 1829--30, 2: 242. Gobius is a genus of gobies.
- f11 7186.f11Crenilabrus massa (the grey wrasse) is now Symphodus cinerea; C. melops (the corkwing wrasse) is now Symphodus melops (Pauly 2004, p. 210).
- f12 7186.f12CD mentions the nests of Crenilabrus, Gobius, and Gasteosterus in Descent 2: 19--20.
- f13 7186.f13CD cited Pierre Carbonnier's view that in almost all fish species, the females were larger than the male, as quoted in the Farmer 1868, p. 369, in Descent 2: 7.