From Benjamin Dann Walsh 13 March 1866
Rock Island. Illinois. U.S. March 13. 1866 Chas. Darwin Esq. My dear Sir,
I send you herewith a copy of a recent Paper for yourself, & another for Mr. Wallace, which I must beg you to forward to him. I do not know & cannot find out his address, or I would not put you to this trouble.1 He was kind enough to send me a copy of his Memoir on the Malayan Papilionidæ, which I am highly delighted with.2
Since my Paper was printed, I have had forwarded to me an extract from Jurine’s “Nouvelle Methode &c” (Tome 1. Introd. p. 19), in which he notices the “bullæ” I have written about as occurring in certain Aculeate Hymenoptera, e.g. Andrena & Nomada among the Bees, though he says Hymenoptera “des deux premièrs ordres n’ont pas de bulles aux ailes, ou s’ils en ont, ce n’est qu’un petit nombre, et elles y sont très-irregulièrement placées.”3 Whereas, after examining hundreds of Eureopean species, belonging to scores of different genera of Ichneumonidæ, besides the N.A. genera already examined, I find that the “bullæ” in any given genus are just as constant & regular as any other generic character, & that the species on the two sides of the Atlantic follow precisely the same laws in this respect.4
Jurine says he was at first inclined to suppose that the ‘bullæ” were apertures through which the air contained in the veins (which he considered as air-tubes) penetrated the membrane of the wing; but that, on reflecting that a very great number of Hymenoptera had no “bullæ” at all, he came to the conclusion that they were caused by the foldings of the wing (les plis de l’aile.)5 But in the first place the wings of Hymenoptera are not folded, in the sense in which the wings of Coleoptera may be said to be folded, & in the second place it is impossible to fold up the wing of an Ichneumon, so as to make a fold wherever there is a “bullæ”, without making additional folds in certain veins which never have any bullæ.
As I find these singular “bullæ” are far more general in Hymenoptera than I had supposed, & wherever they appear are homologous, I partly incline now to believe that they must be connected in some unknown manner with the circulatory system.6 At all events in certain genera, e.g. Metopius & Xylonomus, very fine fibres seem to issue cross-wise from them into the membrane of the wing. But even if we make this assumption, I do not see that this explains the colorational phenomena, i.e. that in a black wing the bullæ & the adjacent membrane should be uniformly white or whitish. It is a very puzzling subject certainly. Singularly enough, Jurine has entirely overlooked what I have called the spots F & G, which are just as plain & constant in the Bee as in the Ichneumon.7
Yours very truly | Benj. D. Walsh
P.S. Do you know anything of a Quaker gentleman, “Mr. Wilson Armistead, Virginia House, Leeds?” He sent me a circular & a letter, stating that he was about to publish an illustrated Book on the Galls of the whole world & soliciting assistance.8 I answered him by Mail last autumn, & afterwards on Oct. 13. 1865 sent him through the Smithsonian Institution a large Box containing specimens of Galls. Since then I have not heard a word from him, which does not strike me as particularly polite. But perhaps he is sick or dead. He stated that he was recommended by Prof. Westwood to apply to me.9
On the "bullae" as constant, regular generic characters in Hymenoptera. Disagrees with Louis Jurine ["Observations sur les ailes des hyménoptères", Mem. Accad. Sci. Torino 24 (1820): 177–214].
Please cite as
Darwin Correspondence Project, “Letter no. 5034,” accessed on 26 September 2016, http://www.darwinproject.ac.uk/DCP-LETT-5034