To B. D. Walsh 27 March 1
Down. | Bromley. | Kent. S.E.
My dear Sir
I have been much interested by your letter.1 I received your former paper on Phytophagic unity, most of which was new to me.2 I have since received your paper on willow-galls: this has been very opportune as I wanted to learn a little about galls.3 There was much in this paper which has interested me extremely, on gradations &c and on your “unity of correlation”.4 This latter subject is nearly new to me, though I collected many years ago some such cases with birds;5 but what struck me most was when a bird-genus inhabits two continents the two sections sometimes display a somewhat different type of colouring. I shd like to hear whether this does not occur with widely ranging insect-genera?
You may like to hear that Wichura has lately published a book which has quite convinced me that in Europe there is a multitude of spontaneous hybrid willows. Wd it not be very interesting to know how the gall-makers behaved with respect to these hybrids?6 Do you think it likely that the ancestor of Cecidomyia acquired its poison like Gnats. (which suck men) for no especial purpose; at least not for gall-making.?7 Such notions make me wish that some one wd try the experiments suggested in my former letter.8 Is it not probable that Guest-flies were aboriginally gall-makers, & bear the same relation to them which Apathus probably does to Bombus?9 With respect to Dimorphism you may like to hear that Dr Hooker tells me that a dioicous parasitic plant allied to Rafflesia has its 2 sexes parasitic on 2 distinct species of the same genus of plants;10 so look out for some such case in the 2 forms of Cynips.11 I have posted to you copies of my papers on Dimorphism.12 Leersia does behave in a state of nature in the provoking manner described by me.13 With respect to Wagner’s curious discovery my opinion is worth nothing:14 no doubt it is a great anomaly, but it does not appear to me nearly so incredible as to you: remember how allied forms in the Hydrozoa differ in their so-called alternate generations: I follow those naturalists who look at all such cases as forms of Gemmation;15 & a multitude of organisms have this power or traces of this power, at all ages from the germ to maturity. With respect to Agassiz’s views there were many, & there are still not a few, who believe that the same species is created on many spots.16 I wrote to Bates & he will send you his mimetic paper, & I dare say others: he is a first rate man.17
Your case of the wingless insects near the Rocky mountains is extremely curious:18 I am sure I have heard of some such case in the old world, I think on the Caucasus. Wd not my argument about wingless insular insects perhaps apply to truly Alpine insects; for wd it not be destruction to them to be blown from their proper home?19 I shd like to write on many points at greater length to you, but I have no strength to spare—
With every good wish believe me yours very sincerely | Charles Darwin
If you publish on wingless insects, kindly inform me or send, if you can, a copy.—
- Letter no.
- Darwin, C. R.
- Walsh, B. D.
- Sent from
- Source of text
- Field Musuem of Natural History, Chicago (Walsh 3)
- Physical description
- 5pp †
Comments on BDW’s papers ["On certain entomological speculations of the New England school of naturalists", Proc. Entomol. Soc. Philadelphia 3 (1864): 207–49; "On insects inhabiting the galls of certain species of willow", ibid. 3 (1864): 543–644]; much is new to CD.
Asks about wide-ranging insect genera,
Rocky Mt. wingless insects,
and other subjects.
Please cite as
Darwin Correspondence Project, “Letter no. 4797,” accessed on 12 February 2016, http://www.darwinproject.ac.uk/DCP-LETT-4797