From Fritz Müller¹ 22 April 1868

Itajahy, S^a Catharina, Brazil

April 22. 1868.

My dear Sir

You must permit me to begin this letter by expressing my sincere and cordial thanks for the great pleasure, which I have derived from the lecture of your admirable work on Variation under Domestication. You say, that the greater part is not meant to be read; but I have read, with increasing interest, the whole work from the first to the last page.—²

As to “Pangenesis”, on which you wish to hear my opinion, my first impression, when for the first time I rapidly read your exposition, was the very same, which I formerly had at the first lecture of your “Origin of species”, viz. that it was a fanciful speculation; but you know, that notwithstanding this first impression I am now fully convinced of the truth of the views maintained in the “Origin”.³ The hypothesis of “Pangenesis” would certainly account for, and connect several great classes of facts hitherto isolated and unexplained; it can also hardly be doubted, that eggs, spermatozoa, ovules of plants and pollengrains, notwithstanding their minute size and apparent simplicity, must be highly complicated structures, containing, as it were, a photograph of the whole organisation, from which they are derived.— But I think, it will be better to delay my objections, till I shall have reflected more maturely on the subject.—

Many thanks for your having published in your second volume my observations on self-sterile Orchids. By the way, there is in your extract a little error, probably due to an error in one of my letters; viz. that Oncidium produced capsules when fertilised with pollen of Leptotes. I have not yet crossed these two genera, but as one belongs to the group of Vandeæ and the other to that of Epidendreæ, I do not think that they will yield capsules, when crossed.⁴

I have to thank you also for your two kind letters of Jan. 30 and Feb 1^st, and for the seeds of Eschscholtzia enclosed in the former.—⁵ As to Cebus, I do not remember, whether he opened his mouth, when astonished.—⁶ I was surprised at hearing, that our Plumbago is an Indian species; it grows on the continent, vis-à-vis Desterro, near the sea-shore, where indeed the seeds may have been introduced with the ballast some ship.⁷

When living on the sea-shore, I did not attend especially to the relative number of the two sexes in marine animals; thus I can give you only very few cases, in which I was struck by the great inequality in their number.

Of the several Diastylidæ (or Cumacea) of S^a Catharina I have invariably caught by far more males than females. Van Beneden has published a paper on this family (in his “Recherches sur la faune littorale de Belgique. Crustaceés.” 1861)⁸ and all the animals described and figured by him I have shown to be males (Archiv für Naturgeschichte, 1865), tho’ he describes some of them as females.—⁹ In the genus Cypridina, of which I observed three species, I have found the males in still greater excess.¹⁰ One day (Novbr. 12. 1865) I caught 63 specimens of one species, of which 57 were males and only 6 females!— The males in this case are smaller than the females.— It is however possible, that the excess of males in both these cases may be only apparent; the males may swim more frequently about in the sea, being thus more easily caught, whilst the females live concealed in the muddy ground; but, tho’ possible, this seems to me not very probable; for I never observed any difference in the behaviour of the two sexes, when held in captivity.—

As to the genus Cypris, W. Zenker, who first described the males, found them on the contrary to be rarer than the females; he says (Studien über die Krebsthiere, 1854):¹¹ “Die Männchen finden sich zu jeder Zeit des Jahres, freilich in geringerer Zahl, neben den Weibchen, scheinen jedoch nach der Abgabe der Zoospermien nicht mehr lange zu leben; denn zeitweise findet man in einzelnen Tümpeln nur samenführende Weibchen.”

In our species of Tanais with the dimorphic males, I have always found the females in considerable excess, and Mr. Spence Bate informed me, that he never caught males of the allied genus Apseudes.¹² But here, as in the case of Cypris, we cannot feel quite sure, that the inequality in the number of the two sexes is a real one. The males of Tanais, being mouthless in their mature state, must of course be much more short-lived, than the females; Zenker, as you have seen, believes that this is also the case with Cypris; and thus, though there live at any time much more females than males, it may be that the two sexes are born in equal number.

In Hippa emerita, that curious inhabitant of sandy shores, the males (as yet undescribed, as far as I know) are much smaller than the females, not reaching half their length; I am almost sure, that I always found the smaller animals in inferior number; among these smaller animals there were of course many young females, so that I have hardly any doubt, that in this species the females are in excess.¹³

On littoral rocks near Desterro, under the oysters and Balanidæ by which they are covered, there lives a Sphæroma interesting by the uncommonly great difference of the two sexes; the female is a true Sphæroma, the male would be, according to Milne Edwards’ classification, a Cymodocea.¹⁴ In most or all other species of the genus there is no external sexual difference. Now the females of that Sphæroma are extremely common; you may easily pick up hundreds in a short time; the males on the contrary are so excessively rare, that I have scarcely caught a few dozens in some years. I do not know, how to explain this extreme inequality in the number of the two sexes; that so few males should be able to fertilize so many females seems quite incredible. The only analogous case, among Crustaceans, I know of, is that of the Phyllopoda and Branchiopoda, the males of some of which are so rare, that they have remained unknown till some years ago, as those of Polyphemus, Apus etc.—¹⁵ Should in Sphæroma also, as is the case with those two orders, the females propagate asexually for many generations?— This would be a great anomaly among higher Crustaceans; but indeed Sphæroma deviates from all other higher Crustaceans by being viviparous, as I first saw in the Sphæroma of the Baltic (Burmeister & D’Alt. Zeitung für Zool. 1849.)¹⁶ and afterwards in several other species and in the allied genus Cassidina.—¹⁷ Or should the Cymodocea-like males lead a different life, and habit a different station, paying but short temporary visits to the females?—

Living, as I do, in a land, where at any hour, winter and summer, day and night, the shrill voices of musical males of Cicadæ, of many Achetidæ, Locustidæ and Acrididæ may be heard, I must really be ashamed of not yet having attended to this subject.¹⁸ I have often been struck—and this is the only thing, I am able to tell you—by a sort of musical contest of two or three males of a large Cicada with a particularly loud voice. They are commonly sitting at a considerable distance from each other and singing alternately; as soon as the first has finished his song, the second immediately begins; after this has concluded, the first begins again and so on.—

Is it not curious that the musical instruments in the males of families so nearly allied, as on the one hand the Achetidæ and Locustidæ, on the other hand the Acrididæ are, should be so different, being in the former placed at the basis of the elytra, whilst the latter use the femur of their hind-legs as a fiddle- stick,—and that at the same time the auditory

.... . Vor einigen Tagen empfing ich einen Brief von meinem Bruder, in dem er mir mittheilt, Sie beabsichtigten meine Schrift “Für Darwin” in England zu veröffentlichen;¹⁹ es ist mir sehr schmeichelhaft, dass Sie mein Buch einer Uebersetzung werth halten.... .

Ich sende Ihnen auch einige Zusätze, betreffend die Entwickelung der Crustaceen und die muthmaassliche Verwandlung von Cirripedien in Rhizocephalen.²⁰ Bezüglich dieser zwei Gruppen darf ich hier Ihre Aufmerksamkeit auf die merkwürdige Thatsache richten, dass deren nahe Verwandtschaft, welche kein Naturforscher hätte vermuthen können, wenn er die voll entwickelten Thiere untersuchte, schon seit langen Zeiten von parasitischen Isopoden erkannt worden ist (wenn der Ausdruck erlaubt ist). Der Parasit, welchen Goodsir als das Männchen von Balanus balanoides beschrieben hat, und von welchem Sie zuerst zeigten, dass er ein weiblicher Isopode ist, gehört nach Herrn Spence Bate zu derselben Gattung Liriope Rethke. (oder Cryptoniscus F. M.), welche an Rhizocephalen lebt.²¹ Ist nun da eine chemische Aehnlichkeit, an welcher diese parasitischen Isopoden die Blutsverwandtschaft der Cirripedien und Rhizocephalen erkennen—oder haben sie schon an Cirripedien gelebt, bevor einige von diesen, an welche sie sich weiter festhefteten, zu Rhizocephalen verwandelt wurden? Ich denke, die letztere Ansicht ist viel wahrscheinlicher, und in diesem Falle würde die Gattung Liriope älter sein als die ganze Gruppe der Rhizocephalen. So können Parasiten wohl in manchen Fällen dazu dienen, das relative Alter verschiedener Thiergruppen zu bestimmen.— Um ein anderes Beispiel zu geben. Es giebt bei Desterro zwei Arten von Renilla, welche oft zusammen an demselben Fleck leben. Eine von Ihnen (Sp. nov.)²² ist sehr häufig heimgesucht von einer sehr merkwürdigen parasitischen Crustacee, welche ihre Eier an die Ovarien legt und deren Larven ihre Verwandlung in den Eiern der Renilla durchmachen. Diesen Parasiten findet man niemals an der zweiten sehr gemeinen Art von Renilla (R. reniformis). Nun ist aber von Brucelius eine nahe verwandte Art unter dem Namen Lamippe rubra als Bewohnerin der europäischen Pennatula rubra beschrieben worden.²³ Unsere Lamippe geht niemals von einer Renilla-Art zur anderen über; sollte wohl früher eine Lamippe von Renilla zu Pennatula übergegangen sein oder umgekehrt? Würde es nicht wahrscheinlicher sein, dass der gemeinsame Vorfahr der Gattungen Renilla und Pennatula diese Parasiten einigen seiner Nachkommen überlieferte? In diesem Falle würde die Gattung Lamippe grade so alt sein als die Familie der Pennatuliden.

Aber ich muss mein langes Gekritzel schliessen und Ihre Verzeihung dafür erbitten. Glauben Sie, werther Herr, dass ich mit aufrichtiger Hochachtung treulichst der Ihrige bin | Fritz Müller.

[Enclosure]

Additions

p. 55, 6 lines from top. Der Schwanztheil des Embryo ist bei den Diastylideen, wie ich neuerlich gesehen habe, nach oben gekrümmt, wie bei den Isopoden, und es fehlt das letzte Fusspaar des Mittelleibes.—²⁴

p. 55, 10 lines from top. Die Entwicklung von Cypris ist neuerdings von Claus beobachtet worden.²⁵ “Die jüngsten Stadien sind schalentragende Nauplius formen.”

p. 64., 15 lines from top.— Wie ich von Mr. C. Spence Bate höre, scheint bei einem Rhizocephalen (Peltogaster?), welchen D^r Powel in Mauritius fand, das Nauplius-stadium übersprungen zu werden und die Larven das Ei als Puppen zu verlassen.—²⁶

p. 65, Anm. 1. According to Mr. C. Spence Bate “the young of Trilobites are of the Nauplius-form”.²⁷

p. 88, foot-note. Ich erhielt neuerdings einen neuen unerwarteten Beweis dafür, dass die Scheerenasseln (Asellotes hétéropodes M. Edw.) unter allen bekannten Krustern der Jetztwelt der Urform der Edriophthalmen am nächsten stehen; Mr. C. Spence Bate schreibt mir: “Apseudes, as far as I know, is the only Isopod in which the antennal scale so common in the Macrura is present in the lower antennæ”.²⁸

p. 90, 9 lines from bottom.²⁹ Ich will nur, als Beispiel, die wahrscheinliche Geschichte der Entstehung einer einzigen Gruppe von Crustaceen geben, und zwar der abnormsten von allen, der Rhizocephalen, die im geschlechtsreifen Zustande so himmelweit selbst von ihren nächsten Verwandten, den Cirripedien, sich entfernen und durch ihre eigenthümliche Ernährungsweise einzig dastehen im ganzen Thierreiche.—

Ich muss einige Worte vorausschicken über die Homologie der Wurzeln der Rhizocephalen, d. h. der Röhren, die vom Anheftungspunkte aus sich in den Leib des Wohnthieres senken, zwischen dessen Eingeweiden sich verästeln und mit blind geschlossenen Zweigelchen endigen. Bei den Puppen der Rhizocephalen (fig. 58) tragen die vordersten Gliedmassen (“prehensile antennæ”) an jedem der beiden Endglieder einen zungenförmigen zarthäutigen Anhang, in welchem man meist einige kleine stark lichtbrechende Körnchen bemerkt, denen ähnlich, die in den Wurzeln des erwachsenen Thieres gesehen werden. Ich habe deshalb in diesen Anhängen die Anfänge der späteren Wurzeln vermuthet. Einen ganz ähnlichen Anhang, einen “most delicate tube or ribbon” fand Darwin bei freischwimmenden Puppen von Lepas australis am letzten Gliede der “prehensile antennæ”.³⁰ Bei der vollkommenen Übereinstimmung die in ihrem ganzen Bau die Puppen des Rhizocephalen und Cirripedien zeigen, kann es keinem Zweifel unterliegen, dass die einander so ähnlichen und an derselben Stelle entspringenden Anhänge von Sacculina und Lepas homologe Gebilde sind.³¹

Bei drei Arten von Lepas, bei Dichelaspis Warwickii und bei Scalpellum Peronii sah nun Darwin, als er seit Kurzem angesiedelte Thiere von der Unterlage losriss, dass von der gleichen Stelle der Antennen ein langes schmales Band ausging, dessen Ende abgerissen war und bei Dichelaspis, nach seinem zerrissenen Aussehen zu schliessen, fest an der Unterlage gehaftet hatte.³² Daraus ergibt sich, dass jener Anhang bei Lepas australis kaum etwas anderes sein kann, als eine junge Kittröhre (“cement-duct”). Ist also die Vermuthung richtig, dass die Anhänge an den Antennen der Rhizocephalen-puppen junge Wurzeln sind, so sind die Wurzeln der Rhizocephalen den cement-ducts der Cirripedien homolog. Und das scheint mir in der That, so befremdlich es auf den ersten Blick sein mag, kaum zweifelhaft. Allerdings ist das Festsetzen des Rhizocephalen noch nicht beobachtet worden; allein es ist mehr als wahrscheinlich, dass sie sich ebenso wie die Cirripedien mittelst der Antennen anheften, dass also die Befestigungspuncte in beiden Gruppen homologe Stellen des Leibes bezeichnen. Vom Befestigungspunct senken sich nun bei den Rhizocephalen die Wurzeln in den Leib des Wirthes, während von da bei den Cirripedien die cement-ducts ausgehen. Die Wurzeln sind blinde Röhren, bei verschiedenen Arten in verschiedener Weise verästelt. Ebenso bilden die cement-ducts in der Basis der Balaniden ein meist ungemein verwickeltes System verästelter Röhren, über deren Endigungsweise noch nichts Sicheres ausgemacht ist. Einzelne blinde Äste sieht man nicht selten selbst in der Nähe der Stämme;³³ und wenigstens bei einigen Arten, bei denen die cement-ducts in ungemein zahlreiche und feine Zweigelchen sich spalten und ein nach dem Umfange der Basis zu immer dichter werdendes Netz bilden, scheinen dieselben überhaupt nirgends eine Öffnung zu besitzen.—

Nun zu der Frage: wie wandelten sich Cirripedien durch natürliche Züchtung in Rhizocephalen um?

Eine beträchtliche Zahl der heutigen Cirripedien siedelt sich ausschliesslich oder vorzugsweise an lebenden Thieren an; an Schwämmen, Corallen, Mollusken, an Walen, Schildkröten, Seeschlangen, Haien, Krustaceen, Seeigeln, ja an Quallen. Dichelaspis Darwinii wurde von Filippi in der Kiemenhöhle von Palinurus vulgaris gefunden und eine andre Art derselben Gattung traf ich in der Kiemenhöhle von Lupea diacantha.³⁴

Ähnliches mag schon in uralter Zeit stattgefunden haben. Die Annahme, dass gewisse Rankenfüsser sich einst die weiche Bauchfläche einer Krabbe einer Porcellana, oder eines Pagurus³⁵ zum Wohnsitze ausersehen hätten, hat gewiss nichts Unwahrscheinliches. Wenn nun die cement-ducts eines solchen Cirripedien, statt nur auf der Oberfläche sich auszubreiten, die weiche Bauchhaut durchbohrend oder vor sich herdrängend ins Innere des Wirthes sich einsenkten, so musste das dem Thiere von Nutzen sein, weil es dadurch sicherer befestigt und gegen Abwerfen beim Häuten des Wirthes geschützt wurde. Abänderungen in dieser Richtung wurden als vortheilhafte erhalten.

Sobald aber cement-ducts in die Leibeshöhle des Wirthes eindrangen und von dessen Leibesflüssigkeit umspült wurden, musste nothwendig ein endosmotischer Austausch zwischen den in dieser Leibesflüssigkeit und den im Inhalte der cement-ducts gelösten Stoffen eintreten und dieser Austausch konnte nicht ohne Einfluss bleiben auf die Ernährung des Schmarotzers. Die auf diese Weise erschlossene neue Nahrungsquelle war als immer fliessend sicherer als die in der zufällig dem Munde des festsitzenden Thieres zugestrudelten Nahrung gebotene. Die in der Entwicklung der zu nahrung-zuführenden Wurzeln umgewandelten cement-ducts bevorzugten Individuen hatten mehr als andere Aussicht auf reichliche Ernährung, auf kräftiges Gedeihen, auf Erzeugung zahlreicher Nachkommenschaft. Mit der so durch natürliche Züchtung geförderten weiteren Ausbildung der den Darm des Wirthes umspinnenden, zwischen seinen Leberschläuchen sich ausbreitenden Wurzeln verlor die Nahrungszufuhr durch den Mund, verloren alle damit in Verbindung stehenden Theile, die strudelnden Ranken, die Mundtheile, der Darm, mehr und mehr an Bedeutung, verkümmerten durch Nichtgebrauch und schwanden zuletzt spurlos. Beschützt durch den Hinterleib der Krabbe, oder durch das Schneckenhaus, in dem der Pagurus lebte, bedurfte der Schmarotzer auch des kalkigen Gehäuses nicht mehr, dessen wahrscheinlich die ersten an jenen Decapoden sich ansiedelnden Cirripedien sich erfreuten. Auch diese überflüssig gewordene schützende Hülle schwand, und es blieb am Ende nur ein weicher mit Eiern gefüllter Sack ohne Gliedmassen, ohne Mund und Nahrungscanal, der sich pflanzenartig durch Wurzeln ernährte, die er in den Leib seines Wirthes getrieben. Aus dem Cirripedien war ein Rhizocephale geworden.

Will man sich eine Vorstellung davon machen, wie etwa unser Schmarotzer mitten auf dem Wege vom Cirripedien zum Rhizocephalen ausgesehen haben möge, so betrachte man die Abbildung, die Darwin (Lepadidæ Pl. IV fig 1–7) von Anelasma squalicola gegeben hat.³⁶ Diese an Haien der Nordsee lebende Lepadide scheint in der That auf bestem Wege zu sein, in ganz ähnlicher Weise seiner Ranken und Mundtheile verlustig zu gehen. Das weitgeschlitzte schalenlose Gehäuse wird von einem dicken Stiele getragen, der in die Haut des Haies eingesenkt ist. Die Oberfläche des Stieles ist besetzt mit stark verästelten hohlen Fäden, welche “penetrate the shark’s flesh like roots” (Darwin). Vergeblich sah sich Darwin nach Cement-drüsen und Cement um.³⁷ Es scheint mir kaum zweifelhaft, dass eben die verästelten hohlen Fäden nichts anderes sind, als zu ernährenden Wurzeln umgewandelte cement-ducts, und dass eben in Folge der Ausbildung dieser neuen Nahrungsquelle Ranken und Mundtheile im höchsten Grade verkümmert sind. Alle Mundtheile sind aüsserst winzig, Palpen und aüssere Kiefer fast verschwunden, die Ranken plump, ungegliedert, borstenlos, die Muskeln der Mundtheile wie der Ranken ohne Querstreifen. Den Magen fand Darwin in dem von ihm untersuchten Thiere völlig leer.—³⁸

CD annotations

1.1 You … ship. 4.6] crossed blue crayon

5.1 When … number. 5.3] crossed blue crayon, ‘Number of Sexes’ added above blue crayon

6.1 Of … females. 6.2] scored blue crayon

6.5 In the genus … excess. 6.7] scored blue crayon

6.7 of which … females!— 6.8] scored blue crayon

6.11 but, tho’ … probable; 6.12] scored blue crayon

8.1 In our … excess, 8.2] scored blue crayon

8.6 Zenker, … number. 8.8] scored blue crayon

10.5 Now … years. 10.8] scored blue crayon

10.10 The only … Branchiopoda, 10.11] scored blue crayon

11.1 Living] after opening square bracket blue crayon

11.1 Living … auditory 12.5] crossed blue crayon

Footnotes

Only a portion of this letter survives in manuscript form. Part of the letter, translated into German, was published in Möller ed. 1915–21, 2: 140. It appears here in the German of the published form. The enclosure was written by Müller mostly in German and the manuscript is now tipped into the front of CD’s copy of F. Müller 1864. For a translation of the German part of the letter and the enclosure, see Correspondence vol. 16, Appendix I.

Müller’s name is on CD’s presentation list for Variation (see Correspondence vol. 16, Appendix IV). See letter to Fritz Müller, 30 January [1868].

For CD’s hypothesis of pangenesis, see Variation 2: 357–404. Müller also refers to Origin.

See Variation 2: 134. Müller had mentioned the genus Leptotes in a letter of 1 December 1866 (Correspondence vol. 14), but had not discussed crossing. Müller discussed his crossing experiments in a letter of 1 April 1867 (Correspondence vol. 15), and sent CD an empty seed-pod from one of the crosses (see Correspondence vol. 15, letter from Fritz Müller, 2 June 1867 and n. 16). Oncidium belongs to the subfamily Vandoideae, while Leptotes is in the subfamily Epidendroideae.

Müller refers to CD’s letters of 30 January [1868] and 11 February 1868. He evidently misread the date of the second letter.

See letter to Fritz Müller, 30 January [1868] and n. 5.

See letter to Fritz Müller, 30 January [1868] and n. 11.

Müller refers to the crustacean family Diastylidae in the order Cumacea, to Pierre-Joseph van Beneden, and to Beneden 1861 (for the section on Cumacea, see pp. 71–87).

See F. Müller 1865, p. 321. Müller was highly critical of van Beneden’s descriptions of cumaceans and used van Beneden’s own illustrations to show that all the specimens were male.

Cypridina is a genus of ostracod crustaceans in the family Cypridinidae.

Cypris is a genus of ostracod crustaceans in the family Cyprididae. Müller refers to Wilhelm Zenker and to an offprint of five articles that first appeared in Archiv für Naturgeschichte, collected under the title Anatomisch-systematische Studien über die Krebsthiere. The quotation is from the first of these articles, ‘Monographie der Ostracoden’ (Zenker 1854, pp. 41–2). Müller’s transcription is correct except for a minor punctuation error. English translation of the extract: There are males at all times of the year, though in smaller numbers, around the females; however, after releasing their sperm they appear not to live much longer; because some of the small ponds occasionally have only seminiferous females.

Müller refers to Charles Spence Bate and to the crustacean genera Tanais (family Tanaidae) and Apseudes (family Apseudidae), both of which are in the modern order Tanaidacea.

Hippa emerita, a synonym of Emerita emeritus is a species found in Asia; Müller evidently intended the South American Emerita brasiliensis.

Sphaeroma and Cymodoce (Cymodocea is an invalid synonym) are isopod crustacean genera of the subfamily Sphaeromatinae, which was named by Henri Milne-Edwards.

Phyllopoda and Branchiopoda were orders of Crustacea; sometimes the latter was considered a sub-order of the former (Ziegler ed. 1909). In modern taxonomy, Phyllopoda is a subclass of the crustacean class Branchiopoda. Polyphemus (suborder Cladocera, water fleas) and Apus (an invalid synonym of Lepidurus, the genus of tadpole shrimp; order Notostraca, fairy shrimp) are phyllopod genera.

Müller refers to a note on Sphaeroma appended to his paper on mating in Clepsine complanata published in Zeitung für Zoologie, Zootomie und Palaeozoologie, a journal edited by Karl Hermann Konrad Burmeister and Johann Samuel Eduard d’Alton (F. Müller 1849).

Cassidina is a genus of the family Sphaeromatidae.

Müller refers to the former insect families Cicadae (now Cicadidae, cicadas), Achetidae (now Gryllidae, crickets), and Locustidae (now subsumed within Acrididae, short-horned grasshoppers).

See n. 1, above. Müller refers to Hermann Müller and to F. Müller 1864. See letter to Hermann Müller, 23 February [1868], and letter from Hermann Müller, [after 23 February 1868].

See enclosure. CD had suggested to Müller that Anelasma squalicola might be a connecting link between cirripedes and the crustacean group Rhizocephala (see Correspondence vol. 13, letters to Fritz Müller, 10 August [1865] and n. 7, and 20 September [1865] and n. 9). Currently, Rhizocephala is a superorder within the infraclass Cirripedia.

Müller refers to Harry Goodsir and to the genus Liriope, originally described by Martin Heinrich Rathke (the misspelling was a printer’s error or mistranscription). Liriope (now Liriopsis) and Cryptoniscus (the genus named by Müller in F. Müller 1864) are both now in the family Cryptoniscidae; they are hyperparasites on species of Rhizocephala. The parasite on Balanus balanoides (now Semibalanus balanoides) first identified by CD is now recognised as Hemioniscus balani, another member of the Cryptoniscidae. For more on Goodsir’s and CD’s identification, see Correspondence vol. 4, letter to Henri Milne-Edwards, 18 November [1847] and nn. 3–5.

‘Species nova’: new species. The species was later named Renilla mulleri (a synonym of R. muelleri) by Rudolf Albert von Kölliker (Kölliker 1869–72, 8: 106–10).

Müller refers to Ragnar Bruzelius (the misspelling was a printer’s error or mistranscription) and to the copepod species Lamippe rubra, found as a parasite on Pennatula rubra (the dark-red sea-pen). See Bruzelius 1859 for a description of the parasite. Müller also refers to the soft coral Renilla reniformis (sea pansy).

Diastilidae is a family of cumacean crustaceans. See F. Müller 1864, p. 55, and W. S. Dallas trans. 1869, pp. 81–2.

For the observation of Carl Friedrich Claus, see Claus 1865, p. 396. See F. Müller 1864, p. 55, and W. S. Dallas trans. 1869, p. 82.

Dr Powel has not been further identified. See F. Müller 1864, p. 64, and W. S. Dallas trans. 1869, p. 95. Peltogaster is a genus of Rhizocephala.

Trilobites were marine arthropods (class Trilobita) that lived between the Cambrian and Permian periods. Most modern classificatory systems place them closer to Chelicerata than to Myriapoda, Crustacea or Hexapoda. Their closest living relative is thought to be the horseshoe crab (class Merostomata). Only crustacean larvae are of the nauplius type.

‘Cheliferous slater’ (‘Scherenassel’ in modern German orthography) is the common name Müller used for the genus Tanais, which he classed as an isopod. ‘Asellotes hétéropodes’, in the classificatory system of Milne-Edwards, was the name of a tribe (which included Tanais) within the family ‘Asellotes’ in the order Isopoda (see Milne-Edwards 1834–40, 3: 141).

W. S. Dallas trans. pp. 135–40.

See Living Cirripedia (1854): 118, 673, and plate 30 fig. 8. Lepas australis is a goose barnacle.

Sacculina is a rhizocephalan.

See Living Cirripedia (1854): 118-19, and plate 30 fig. 8. Dichelaspis Warwickii is a synonym of Octolasmis warwickii, and Scalpellum Peronii is a synonym of Smilium peronii.

Dallas incorrectly translated ‘in der Nähe der Stämme’ as ‘in the vicinity of the carina’ (see W. S. Dallas trans. 1869, p. 137); CD underlined the word ‘carina’ and put a question mark in the margin of his copy, which is in the Rare Books Room–CUL (see Marginalia 1: 609). CD described and figured the ‘cement-trunk’ in Living Cirripedia (1854): 668 and plate 28, fig. 1c.

Müller refers to Filippo De Filippi and De Filippi 1861, p. 71. Dichelaspis Darwinii is now Octolasmis darwini; Palinurus vulgaris is now Palinurus elephas (the common spiny lobster); Lupa diacantha (‘Lupea’ is an incorrect subsequent spelling) is now Callinectes sapidus (the blue crab).

Porcellana is a porcelain crab; Pagurus is a right-handed hermit crab.

Living Cirripedia (1851).

See Living Cirripedia (1851): 173–4.

See Living Cirripedia (1851): 177.

Bibliography

Beneden, Pierre Joseph van. 1861. Recherches sur les crustacés du littoral de Belgique. Mémoires de l’Académie Royale des Sciences, des Lettres, et des Beaux-Arts de Belgique 33: 1–174.

Bruzelius, R. 1859. Ueber einen in der Pennatula rubra lebenden Schmarotzer. Archiv für Naturgeschichte 25, pt. 1: 286–90.

Claus, Carl Friedrich. 1865. Zur näheren Kenntniss der Jugendformen von Cypris. Zeitschrift für wissenschaftliche Zoologie 15: 391–7.

Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.

Living Cirripedia (1851): A monograph of the sub-class Cirripedia, with figures of all the species. The Lepadidæ; or, pedunculated cirripedes. By Charles Darwin. London: Ray Society. 1851.

Living Cirripedia (1854): A monograph of the sub-class Cirripedia, with figures of all the species. The Balanidæ (or sessile cirripedes); the Verrucidæ, etc. By Charles Darwin. London: Ray Society. 1854.

Marginalia: Charles Darwin’s marginalia. Edited by Mario A. Di Gregorio with the assistance of Nicholas W. Gill. Vol. 1. New York and London: Garland Publishing. 1990.

Milne-Edwards, Henri. 1834–40. Histoire naturelle des crustacés, comprenant l’anatomie, la physiologie et la classification de ces animaux. 4 vols. Paris: Librairie encyclopédique de Roret.

Müller, Fritz. 1849. Ueber die Begattung der Clepsine complanata Sav. (Glossiphonia sexoculata Moq. Tand. Monogr. ed. 2). Zeitung für Zoologie, Zootomie und Palaeozoologie 1: 197–9.

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

Zenker, Wilhelm. 1854. Monographie der Ostracoden. Archiv für Naturgeschichte 20, pt 1: 1–87.

Translation

From Fritz Müller¹ 22 April 1868

.... . . Several days ago I received a letter from my brother in which he informed me that you intended to publish my book “Für Darwin” in England;² it is a great compliment to me that you consider my book worth translating.... .

I am also sending you a few addenda relating to the development of crustaceans and the conjectured transformation from cirripedes to rhizocephalans.³ In reference to those two groups may I direct your attention to the remarkable fact that their close relation, which no naturalist could have suspected if he studied the fully developed animals, was already recognised (if we allow the expression) a long time ago by parasitic isopods. The parasite that Goodsir described as the male of Balanus balanoides and that you first showed to be a female isopod, belongs according to Mr. Spence Bate to the same genus Liriope Rethke. (or Cryptoniscus F.M.) that lives on Rhizocephala.⁴ Is there then a chemical resemblance by which those parasitic Isopods recognise the blood relationship of cirripedes and rhizocephalans—or were they already living on cirripedes before a few of the latter, on which they fastened themselves, were transformed into rhizocephalans? I think the latter view is much more probable, and in that case the genus Liriope would be older than the whole group of rhizocephalans. In this way parasites could well serve in many cases to determine the relative ages of different groups of animals.— To give another example. There are near Desterro two species of Renilla that often live together in the same spot. One of them (Sp. Nov.)⁵ is very frequently infested by a most remarkable parasitic crustacean which lays its eggs on the ovaries, and the larvae of which go through metamorphosis in the eggs of Renilla. That parasite is never found on the second very common species of Renilla (R. reniformis). A closely related species by the name of Lamippe rubra has, however, now been described by Brucelius as an inhabitant of the European Pennatula rubra.⁶ Our Lamippe never passes over from one Renilla species to the other; could a Lamippe perhaps earlier have gone over from Renilla to Pennatula or vice versa? Would it not be more likely that the common ancestor of the genera Renilla and Pennatula passed on those parasites to some of its descendants? In that case the genus Lamippe would be just as old as the pennatulid family.

But I must close my long scribble and beg your pardon. Believe, dear Sir, that I am with sincere admiration most faithfully yours | Fritz Müller.

Additions

p. 55, 6 lines from top. The caudal part of the embryo in the diastylids, as I have recently observed, is curved upwards as in isopods, and the last pair of feet on the thorax is missing.—⁷

p. 55, 10 lines from top. The development of Cypris has recently been observed by Claus.⁸ “The youngest stages are shell-bearing Nauplius forms.”

p. 64, 15 lines from top.— As I learn from Mr. C. Spence Bate, a rhizocephalan (Peltogaster?) which Dr. Powel found in Mauritius appears to skip the Nauplius stage and the larvae leave the eggs as pupae.⁹

p. 65, note 1. According to Mr. C. Spence Bate “the young of Trilobites are of the Nauplius-form”.¹⁰

p. 88, foot-note. I recently obtained a new and unexpected proof that the cheliferous slaters (Asellotes hétéropodes M. Edw.) resemble the ancestral form of edriophthalmians more closely than any other known present-day Crustaceans; Mr. C. Spence Bate informs me that: “Apseudes, as far as I know, is the only Isopod in which the antennal scale so common in the Macrura is present in the lower antennæ”.¹¹

p. 90, 9 lines from bottom.¹² I will only give, as an example, the probable history of the origin of a single group of crustaceans, and indeed of the most abnormal of all, the rhizocephalans, which in the sexually mature state differ so completely even from their nearest relatives, the cirripedes, and, from their peculiar mode of feeding, stand alone in the entire animal kingdom.—

I must say a few prefatory words on the homology of the roots of rhizocephalans, i.e. the tubules that penetrate from the point of attachment into the body of the host animal, branching out in the intestines of the latter and terminating in blind (caecal) branchlets. In the pupae of rhizocephalans (fig. 58), the foremost limbs (“prehensile antennæ”) bear on each of the two terminal joints a tongue-shaped, thin-skinned appendage in which one can usually observe a few strongly refractive granules, which are similar to those in the roots of the adult animal. I have therefore supposed these appendages to be the rudiments of future roots. Quite a similar appendage, a “most delicate tube or ribbon”, was found by Darwin in the free-swimming pupae of Lepas australis on the last joints of the “prehensile antennæ”.¹³ From the complete correspondence shown in the entire structure of the pupae of rhizocephalans and cirripedes, there can be no doubt that the appendages of Sacculina and Lepas, which are so similar and spring from the same point, are homologous structures.¹⁴

In three species of Lepas, in Dichelaspis Warwickii and in Scalpellum Peronii, Darwin saw, as he tore the recently-affixed animals from their support, that a long narrow band emanated from the same part of the antennae; its end was torn away, and in Dichelaspis, judging from its ragged condition, had been firmly fastened to the support.¹⁵ From this it follows that this appendage in Lepas australis can hardly be anything but a young cement tube (“cement duct”). If, then, the supposition is correct that the appendages on the antennae of the rhizocephalan pupae are young roots, then roots of rhizocephalans are homologous with the cement-ducts of cirripedes. And indeed it seems to me, however strange this may appear at first glance, hardly doubtful. Of course, the process of attachment in rhizocephalans has not yet been observed; but it is more than likely that they, just like cirripedes, attach themselves by means of their antennae, and that therefore the points of attachment in both groups signify homologous parts of the body. From the point of attachment the roots in rhizocephalans penetrate into the body of the host, while from here in cirripedes the cement-ducts emanate. The roots are caecal tubes, which in different species branch out in different ways. Likewise, the cement ducts in the basis of balanids form an unusually complicated system of ramified tubes; nothing certain has yet been ascertained about their manner of termination. Individual blind branches are not infrequently found near the trunk;¹⁶^ and at least in some species, whose cement-ducts divide into uncommonly numerous and fine branchlets, forming a network that gradually becomes denser towards the circumference of the basis, these ducts overall seem nowhere to possess an orifice.—

Now as to the question: how were cirripedes converted into Rhizocephala by natural selection?

A considerable number of existing cirripedes settle exclusively or primarily upon living animals, on sponges, corals, molluscs, on whales, turtles, sea snakes, sharks, crustaceans, sea urchins, even medusas. Dichelaspis Darwinii was found by Filippi in the gill cavity of Palinurus vulgaris and I came across another species of the same genus in the gill cavity of Lupea diacantha.¹⁷

The same thing may well have happened in ancient times. The assumption that certain barnacles once chose the soft ventral surface of a crab, Porcellana, or Pagurus¹⁸ for a dwelling place, certainly has nothing improbable about it. If then the cement ducts of such a cirripede, instead of merely spreading over the surface, pierced or pushed aside the soft ventral skin and penetrated into the interior of the host, this must have been beneficial to the animal, because it would thereby be more securely attached and protected from being cast off during the molting of the host. Variations in this direction were preserved as advantageous.

But as soon as the cement ducts penetrated into the body cavity of the host and were bathed by its fluids, an endosmotic exchange between the substances dissolved in these fluids and in the contents of the cement ducts must necessarily have taken place, and this exchange could not be without influence on the nourishment of the parasite. The new source of nourishment unlocked in this way was, since constantly flowing, more certain than that offered by the nourishment that accidentally swirled into the mouth of the sedentary animal. The individuals favoured with cement ducts transformed into roots that supplied nutrition had, more than others, the prospect of abundant food, of vigorous growth, of producing numerous offspring. With the further development, stimulated by natural selection, of the roots that entangled the intestine of the host and spread out through its hepatic tubes, feeding through the mouth was lost and with it all related parts, the whirling cirri, the mouthparts, the intestine, gradually lost their importance through lack of use, degenerated, and finally disappeared without a trace. Protected within the abdomen of the Crab, or by the shell in which Pagurus lived, the parasite also no longer required the calcareous casing which the first cirripedes that settled on these decapods probably enjoyed. This protective covering, having become superfluous, also disappeared, and there remained in the end only a soft sack filled with eggs, without limbs, without mouth and alimentary canal, which was nourished like a plant, by means of roots that it pushed into the body of its host. The cirripede had become a rhizocephalan.

To get an impression of what our parasite may have looked like when half way in its progress from the one form to the other, we may consult the figures given by Darwin (Lepadidæ Pl. IV fig. 1--7) of Anelasma squalicola.¹⁹ This lepadid, which lives upon North Sea sharks, seems in fact to be well on its way to losing its cirri and mouthparts in the same manner. The widely-cleft, shell-less casing is supported upon a thick peduncle, which is immersed into the skin of the shark. The surface of the peduncle is crammed with densely branching, hollow filaments, which “penetrate the shark's flesh like roots” (Darwin). Darwin looked in vain for cement glands and cement.²⁰ It seems to me hardly doubtful that the branching hollow filaments themselves are none other than cement ducts converted into nutritive roots, and that it is just as a result of the development of this new food source that the cirri and mouthparts have degenerated to the greatest extent. All the mouthparts are extremely minute; the palpi and exterior maxilla have almost disappeared; the cirri are heavy, inarticulate, and destitute of setae; and the muscles of the mouthparts as well as the cirri are without transverse striation. Darwin found the stomach completely empty in the animal examined by him.—²¹

Footnotes

Only a portion of this letter survives in manuscript form. Part of the letter, translated into German, was published in Möller ed. 1915–21, 2: 140. The enclosure was written by Müller mostly in German and the manuscript is now tipped into the front of CD’s copy of F. Müller 1864. For the transcription of the German of the published part of the letter and the original German of the enclosure, see part I: 435–9.