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Darwin Correspondence Project

From B. D. Walsh   29 May 1865

Rock Island. Illinois. May 29, 1865 Chas. Darwin Esq My dear Sir,

Many thanks for your letter of March 27.1 I fear, in the present state of your health, I am troubling you too often with my scribblings; but the remedy is an easy one & in your own hands—throw them in the fire.

I was delighted with your Linum & Primula papers, & also with Mr. Scott’s paper on Primulaceæ.2 What a remarkable fact that is which he brings out, that the red variety of the common Primrose absolutely refuses to intercross with the normal form.3 Such facts as these, it seems to me, knock the ground away completely from under the Creative Theory.

As to “Unity of Coloration” you have yourself given one very good example in the stripes which re-appear more or less in the several species of the genus Equus. 4 Another instance is found in the fawn of our common deer being spotted like many adult fallow deer, & Prof. Haldeman5 writes me word that he has remarked on the rump in cervus & antelope “being frequently of a lighter tint than the general color”. (Freshwater Univalve Mollusca No 7. Jan 1844 Planorbis p. 5)6   There is another most remarkable one in the Owlet-moths (Noctuadæ), in almost every genus of which the “orbicular” & “reniform” spots are found, besides five transverse lines of color which Guenée calls respectively the “basal”, the “transverse anterior”, the “transverse posterior”, the “subterminal” & the “terminal”.7 From the enormous number of species in Insects, an Entomologist is naturally led to notice such things more than other Naturalists. I am not sufficiently familiar with exotic species of Insects to say whether or not genera inhabiting two continents “sometimes display a somewhat different type of coloring”.8 But ever since I have been collecting in this country I have been struck almost every day by the same genera on both sides the Atlantic displaying the same coloration. For example, I have two N.A. species of Panagæus in my collection, (P. fasciatus Say, & cruciger Say) which imitate your P. crux-major both in design & color; yet with the exception of the Lebia & Bembidium groups, almost all other Carabidæ are of plain colors. If then there is no genetic connection between the N.A. & European species of Panagæus, & if (as I think we must concede) coloration is independent of structure, why should Panagæus, on both sides of the Atlantic, have four more or less confluent large red spots arranged in a quadrangle on its elytra?

My idea as to the mode in which Cecidomyia acquired its gall-producing poison,9 is that originally they were all without it, as are to this day the Hessian fly (C. destructor) & the Wheat-midge. (Cec. tritice). But that individuals by Variation acquired the power of secreting a minute portion of poison so as to irritate the plant slightly & cause a slight additional flow of sap, & a better nidus for the future larva,, whereby they gained an advantage over their fellows & so on according to your theory. Whether the Guest-flies are degraded Gall-flies, or in an incipient state of perfection, is perhaps a doubtful point, though I rather incline to the former hypothesis.10

As to Wagner’s theory of Viviparous larvæ,11 allowing it as you say to be a form of gemmation, ought we to expect to find a mode of reproduction characteristic of the Vegetable Kingdom, & hitherto only met with in Animals of very low type, in such highly organized & intellectual beings as Insects? Taking everything into consideration, I think Insects are superior to Fish, & could you yourself swallow down gemmiparous Fish without very good Ichthyological authority? I couldn’t. Now if a Fish, which has no “penis intrans”,12 which inhabits the water still & which still breathes through gills, is not found to be gemmiparous, I am loath to believe that an insect can be so. Still, facts are stubborn things, & it may turn out that Wagner & Co are right, though I still believe he was deceived by parasitic larvæ.13

In a brief review of Wagner’s book which I have lately seen reference is made to a genus Daphnia & Family Daphnidæ, in which both males & females are said to produce parthenogenic eggs in the summer, & another kind of eggs called “ephippia” in the winter.14 To what class do these extraordinary animals belong? Can it be possible that true males generate eggs?

I bought a few weeks ago Lyell’s Book on the Antiquity of Man,15 & was highly delighted with it. I had no idea that Prof. Owen was capable of making such an ass of himself as he has done16section excised

You have referred in the “Origin” to a (dipterous?) fly checking the propagation of cattle & horses in the southern parts of South America.17 I find that in Gen. Páez’s book on South America (p. 58) he says that in the Northern parts (Venezuela &c) a fly called ‘gutano’ oviposits in the umbilicus of newly born foals so constantly, that the herdsmen have to examine all the young foals & remove the larva, or otherwise the foal is sure to die.18 May we not account for the extinction of the Horse in America by some such means as this?

Ever yours very truly, | Benj. D. Walsh

section excised〉 the so-called 〈remainder of line excised〉 I am as unwilling to believe in gemmiparous insects as in hermaphrodite insects. Both seem to me low forms of reproduction derived originally from the Vegetable Kingdom & dropped in the march of development at an early period.

CD annotations

4.1 My idea … larvæ. 5.11] crossed pencil
8.3 he says that … as this? 8.7] scored pencil; ‘Struggle for Existence’ added pencil
On separate sheet: ‘Unity of colour in Bembycidæ— | Panagæus in N. America coloured as in Europe—good | Law of Variation | My analogy of variation is nearly same as Walsh law of equable coloration, only I refer only to Variation’19 pencil


CD had sent Walsh copies of ‘Dimorphic condition in Primula, ‘Two forms in species of Linum (see letter from B. D. Walsh, 1 March 1865, and letter to B. D. Walsh, 27 March [1865]), and, evidently, an offprint of John Scott’s study of reproduction in the Primulaceae (Scott 1864b).
In Scott 1864b, pp. 97–102, Scott gave the results of experiments with Primula vulgaris, the common primrose, and a red and a white variety of primrose. His results suggested that the red primrose was infertile with pollen from the common and the white primrose, but fertile with its own pollen. If established, this would have been evidence in favour of CD’s views on the origin of species. Thomas Henry Huxley, in several publications (most recently in T. H. Huxley 1863b), had argued that CD’s views would not be beyond doubt until he could demonstrate ‘the possibility of developing from a particular stock, by selective breeding, two forms, which should either be unable to cross one with another, or whose cross-bred offspring should be infertile with one another’ (T. H. Huxley 1863b, p. 146). CD had also thought that Scott’s results were remarkable (see Correspondence vol. 12, letter to Asa Gray, 13 September [1864]). However, he was unable to corroborate Scott’s results regarding the sterility of the red variety when pollinated by the common primrose when he repeated the crossing experiments in 1865 and 1866 (see Variation 2: 109 n. and ‘Illegitimate offspring of dimorphic and trimorphic plants’, p. 420). CD’s notes on these experiments are in DAR 108 and DAR 110. For further discussion of CD’s and Scott’s experimental work on intra-specific sterility, prompted by Huxley’s challenge, see Correspondence vols. 10–12.
For CD’s interest in Walsh’s law of unity of coloration, see his letter to Walsh of 27 March [1865] and nn. 5 and 6. In Origin, pp. 163–7, CD gave examples of the tendency of a number of species in the horse genus to develop stripes, especially in young animals and hybrids, and hypothesised that this was because they were descended from a striped ancestor. See also Correspondence vols. 7–9.
Samuel Steman Haldeman.
In his Monograph of the freshwater mollusca of the United States, Haldeman, in a discussion of Planorbis, a genus of pond-snails, commented: ‘Certain uniform colors, lines, or spots, mark genera and families; in Cervus and Antilope the rump is frequently of a lighter tint than the general color’ (Haldeman 184[2–]5, ‘Genus Planorbis, Müller’, p. 5).
Walsh probably refers to Achille Guenée’s three-volume monograph on the Noctuadae or ‘Noctuélites’ (Guenée 1852). Guenée’s terminology for describing the spots and lines of colour on the wings of this family of moths appears in Guenée 1852, 1: xlii–xliv and 3: fig. 1; however, Walsh appears to have translated Guenée’s terms into a nomenclature of his own.
For CD’s query as to whether guest-flies may have developed from gall-flies, and for Walsh’s subsequent discussion in Walsh 1866, see the letter to B. D. Walsh, 27 March [1865] and n. 10.
For CD’s comment on Nikolai Petrovich Wagner’s observation of paedogenesis (Wagner 1862 and 1863), see the letter to B. D. Walsh, 27 March [1865] and nn. 15 and 16.
Penis intrans: internal penis (C. T. Lewis and Short 1969).
For Walsh’s eventual conclusion regarding paedogenesis, see the letter to B. D. Walsh, 19 December [1865], and Walsh 1866, p. 288.
The reference is to the review of Wagner’s article on viviparous gall-forming midge larvae (Wagner 1865) in the May 1865 issue of the American Journal of Science and Arts, pp. 362–3 (Minor 1865). Walsh was misled by a mistake in translation in the review. Wagner had drawn an analogy between the two phases of reproduction in Aphis and Daphnia. In both genera, males and females are produced asexually by parthenogenetic eggs in summer; they are also produced sexually in winter from eggs carried by the female in a pouch, or ephippia (Wagner 1865, pp. 110–11). The review of Wagner 1865, however, mistranslated reproduction ‘of both males and females’ as reproduction ‘in both males and females’, thus implying that males produced eggs (Minor 1865, p. 362).
Walsh probably refers to the second American edition of Charles Lyell’s Antiquity of man (C. Lyell 1863d).
In Antiquity of man, Lyell reviewed the long-running controversy between Richard Owen and, principally, Thomas Henry Huxley about the comparative anatomy of human and simian brains (C. Lyell 1863a, pp. 480–93). On the so-called hippocampus controversy, see A. Desmond 1982, Rupke 1994, and L. G. Wilson 1996. See also Correspondence vols. 9–11.
Walsh refers to Origin, p. 72.
The reference is to Ramón Páez’s Wild scenes in South America, or life in the llanos of Venezuela (Paez 1863, pp. 58–9). Páez was a son of General José Antonio Páez (see letter from B. D. Walsh, 12 November 1865).
On Walsh’s law of unity of coloration, see n. 4, above. For CD’s discussion of analogous variation (the tendency of descendants of a common ancestor to vary in similar ways), see Origin, pp. 159–70, and Variation 2: 348–52. In Variation 2: 351–2, CD mentioned Walsh’s ‘Law of Equable Variability’: ‘if any given character is very variable in one species of a group, it will tend to be variable in allied species; and if any given character is perfectly constant in one species of a group, it will tend to be constant in allied species’ (Walsh 1863, p. 213); adding that this law was similar to his statement in Origin that generic characters were less variable than specific characters (see Origin, p. 168). CD also comments on Walsh’s law of equable variability in Origin 4th ed., p. 187.


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 27 vols to date. Cambridge: Cambridge University Press. 1985–.

Desmond, Adrian. 1982. Archetypes and ancestors: palaeontology in Victorian London, 1850–1875. London: Blond & Briggs.

‘Dimorphic condition in Primula’: On the two forms, or dimorphic condition, in the species of Primula, and on their remarkable sexual relations. By Charles Darwin. [Read 21 November 1861.] Journal of the Proceedings of the Linnean Society (Botany) 6 (1862): 77–96. [Collected papers 2: 45–63.]

Guenée, Achille. 1852. Noctuélites. Vols. 5–7 of Histoire naturelle des insectes: species général des lépidoptères, by Jean Baptiste Alphonse Boisduval and Achille Guenée. Paris: Librairie Encyclopédique de Roret.

‘Illegitimate offspring of dimorphic and trimorphic plants’: On the character and hybrid-like nature of the offspring from the illegitimate unions of dimorphic and trimorphic plants. By Charles Darwin. [Read 20 February 1868.] Journal of the Linnean Society of London (Botany) 10 (1869): 393–437.

Minor, W. C. 1865. Further remarks on larve budding. American Journal of Science and Arts 2d ser. 39: 362–3.

Origin 4th ed.: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. 4th edition, with additions and corrections. By Charles Darwin. London: John Murray. 1866.

Origin: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. By Charles Darwin. London: John Murray. 1859.

Paez, Ramon. 1863. Wild scenes in South America, or life in the llanos of Venezuela. 2d edition. New York: Charles Scribner.

Rupke, Nicolaas A. 1994. Richard Owen, Victorian naturalist. New Haven, Conn., and London: Yale University Press.

‘Two forms in species of Linum’: On the existence of two forms, and on their reciprocal sexual relation, in several species of the genus Linum. By Charles Darwin. [Read 5 February 1863.] Journal of the Proceedings of the Linnean Society (Botany) 7 (1864): 69–83. [Collected papers 2: 93–105.]

Variation: The variation of animals and plants under domestication. By Charles Darwin. 2 vols. London: John Murray. 1868.

Wagner, Nikolai Petrovich. 1865. Uber die viviparen Gallmückenlarven. Zeitschrift für wissenschaftliche Zoologie 15: 106–15.


Discusses several subjects, including examples of "Unity of coloration",

the origin of gall-producing poison,

Wagner’s theory of viviparous larvae,

and stridulation in insects.

Sends a reference supporting CD’s statement in Origin that flies check propagation of horses and cattle.

Letter details

Letter no.
Benjamin Dann Walsh
Charles Robert Darwin
Sent from
Rock Island, Ill.
Source of text
DAR 47: 179, 179a; DAR 207: 18
Physical description
4pp inc †, CD note

Please cite as

Darwin Correspondence Project, “Letter no. 4839,” accessed on 29 February 2020,

Also published in The Correspondence of Charles Darwin, vol. 13