The only extended word for word citation in Finnegans Wake is the following:

Aujourd’hui, comme aux temps de Pline et de Columelle, la jacinthe se plaît dans les Gaules, la pervenche en Illyrie, la marguerite sur les ruines de Numance; et, pendant qu’autour d’elles les villes ont changé de maîtres et de nom, que plusieurs sont entrées dans le néant, que les civilisations se sont choquées et brisées, leurs paisibles générations ont traversé les âges et se sont succédé jusqu’à nous, fraîches et riantes comme au jour des batailles. (FW 281)

Today, as in the days of Pliny and Columella, the hyacinth disports in Gaul, the periwinkle in Illyria, the daisy on the ruins of Numantia; and while around them the cities have changed masters and names, while some have ceased to exist, while the civilisations have collided with one another and shattered, their peaceful generations have passed through the ages, and have come up to us, one following the other, fresh and cheerful as on the days of the battles.

Joyce was quoting the French historian Edgar Quinet (1803-75), from Introduction à La Philosophie de l’Histoire de l’Humanité (1857), via the naturalist, Léon Metchnikoff (1838-1888),  who cited Quinet in his La Civilisation et les Grands Fleuves Historiques (1889). Joyce read Metchnikoff’s book in 1924. As nicely set out in the From Swerve of Shore to Bend of Bay blog from which the above translation is taken, Joyce used the Quinet text over and over again in FW and was known to cite it by heart in his conversation. Peter Chrisp, the Swerve of Shore blogger, describes how:

Joyce summed up the [Edgar Quinet] sentence in a letter to Harriet Shaw Weaver: ‘E.Q. says that the wild flowers on the ruins of Carthage, Numancia etc have survived the political rises and falls of Empires’ (L1: 295).  Quinet uses classical Rome as the example of empire. Pliny the Elder and Columella were the great Roman writers on nature: Pliny wrote a massive Natural History and Columella wrote books on Agriculture and Trees. Numantia was a city in Spain whose inhabitants committed suicide rather than surrender to the Romans. Illyria in the western Balkans and Gaul (France) were also conquered by Rome.
Joyce said he ‘felt at home’ in this sentence. He shared Quinet’s detached view of history, eternally repeating the same events. (…). In later life, says [Richard] Ellmann [in his biography of Joyce], [Samuel] Beckett ‘thought this ability to contemplate with telescopic eye Joyce’s most impressive characteristic, and quoted four lines from Pope’s ‘Essay on Man’ to illustrate:
Who sees with equal eye, as God of all,
A hero perish, or a sparrow fall,
Atoms of systems into ruin hurled,
And now a bubble burst, and now a world.’  (Ellmann, James Joyce, 1982, 709)

The same Quinet citation is treated in How Joyce Wrote Finnegans Wake: A Chapter-by-chapter Genetic Guide, ed Luca Crispi and Sam Slote (2007), where it is seen as central to the involuted structure of the entire book:

the turning point for [the FW character] Shaun [the post], and indeed for Finnegans Wake [as a whole], came when Joyce read a book by Leon Metchnikoff, La Civilisation et les Grands Fleuves Historiques. Metchnikoff describes Giambattista Vico’s cyclical theories of corsi and ricorsi as the underlying dynamic for historical progress. Joyce had already been interested in Vico, but this book seemed to have energized his thoughts on the matter and especially on how he could deal with Shaun. The delivery of the letter is no longer a single episode in the saga of HCE but rather a repetition and recapitulation, “by a commodious vicus of recirculation” (FW: 003.02), of that saga into a different register. Shaun’s delivery of the letter replays HCE’s downfall, which is what is recorded, somehow, in the letter itself. The discovery of Shaun’s role could thus be seen as the final nail in the coffin of Wakean narrative as “goahead plot” (LIII: 146).  With Book III Wakean narrative turns back on itself to repeat “the seim anew” (FW: 215.23). If Book I could be said to move forward in the explication of HCE’s fate, then Book III moves backward. As Joyce explained to Weaver, the first part of Book III “is a description of a postman travelling backwards in the night through events already narrated. It is written in the form of a via crucis of 14 stations but is actually only a barrel rolling down the river Liffey” (LI: 214). What Joyce had been experimenting with at the local level with the textual reverberations emanating from the [post-Ulysses] sketches (…) has now, with the invention of Shaun, become the organizing structural principle for the work as a whole.
Another element Joyce derived from Metchnikoff’s book is a quotation from the French philosopher of history Edgar Quinet’s book Introduction à La Philosophie de l’Histoire de l’Humanité  (…). It is clear that Joyce derived the quote from Metchnikoff, since he reproduces Metchnikoff’s errors. The sentence describes the effects of temporal change, and Joyce described it as “beautiful” (LI: 295). The sentence was ultimately to take on a kind of nodal resonance as it wound up being incorporated into the [FW] text six times with varying degrees of Wakean distortion. (‘Introduction’, 19-20)

“Temporal change” at the end of this passage is a surprising singular, since the central point of the Quinet sentence would seem to be the contrasting times in the lives of cities and whole civilisations compared to that of flowers. The chapter of FW, in which the Quinet citation appears in its word for word form, features marginal notes from Joyce.  Next to the citation appears:

THE PART PLAYED BY BELLETRISTICKS IN THE BELLUM-PAX-BELLUM.
MUTUOMORPHOMUTATION. (FW 281)

The time of the mutuomorphomutation of cities, empires and civilizations — and, indeed, of “belletristicks” like Shem’s and Joyce’s own efforts — is not the time of flowers nor that of mutuomorphomutation itself. The latter times, although not without their own dynamic rhythms, are synchronic (always in play, always about to bloom again and again, regenerating themselves in and through death), while the former are diachronic and definitively subject to death.  Identity in the former infolds ‘passing away’; in the latter ‘passing away’ is — ‘passing away’.

These contrasting times are particularly focused in Joyce’s note: BELLUM-PAX-BELLUM. On the one hand, this could be taken in the “register” of “goahead plot” or diachronic law: this is time’s arrow to which cities, empires and civilizations, along with belletristicks, are subject. On the other, BELLUM-PAX-BELLUM could be read as the synchronic spectrum of being itself, a triple form which human beings have always already witnessed (although nearly always in “blackout” mode) traversing their perpetual ano-kato pathway in the genesis of experience.

Now McLuhan imagined this synchronic process in terms of Poe’s Maelstrom.  On this model, human beings are at every moment subject to a katabasis into a “worldpool” of warring forms — BELLUM-PAX-BELLUM — from which they emerge, or have always already emerged, into their momentary experience, like Poe’s mariner riding a “barrel” to the surface of the sea out of the Maelstrom whirlpool.

Consideration of this process led to McLuhan’s stipulation in Take Today:

There are only two basic extreme forms of human organization. They have innumerable variants or “parti-colored” forms. The extreme forms are the civilized and the tribal (eye and ear): the Cromwellian specialist and the Celtic involved. Only the civilized form is fragmented in action…(22; the bracketed insertion of “eye and ear” is from McLuhan)

Compare Joyce in conversation with Georges Borach fifty years before in 1918:

There are indeed hardly more than a dozen original themes in world literature. Then there is an enormous number of combinations of these themes.¹

The advance from “two basic extreme forms” (eye/ear) to three, BELLUM-PAX-BELLUM (aka eye-ear-eye), occurs through the fact that BELLUM, as the word itself indicates, and as its doubling (Dublin) in BELLUM-PAX-BELLUM makes explicit, is “fragmented in action”. Its warring sides each claim fundamental priority and exactly therefore eternally battle against the other in an endless attempt to establish a singular priority for themselves alone. Considered synchronistically, where “all is always now”, such a war of archetypal forms can have no end. Both of its sides must be equally original and, therefore, unknown to themselves, behind their backs so to say, subject to a kind of PAX as their mutual right to be a part (or “station”) of the archetypal order. To wage their endless war, they must be double, but with a common standing.

The further advance from 2 and 3 to “hardly more than a dozen” is generated through the fact that BELLAM, as a contesting power that is “fragmented in action”, is subject to degree. The opposition between the belligerent sides ranges along the archetypal spectrum from the avowed obliteration of the other at the extremes of their mutual antagonism to the PAX of mutual recognition where the two meet in the middle of the range. 

In short, the archetypal powers are arrayed in along a spectrum whose double ends (Dublin) tend toward the maximum antagonism of the warring sides (BELLUM-BELLUM) and whose middle represents their PAX. The Gutenberg Galaxy would tell the tale of the diachronic ascendancy of BELLUM over PAX over the last 500 years and begin the exposition in its concluding section of ‘The Galaxy Reconfigured’ in the ‘electric age’ today.²

Considering the perpetual exposure to the forms of being in the genesis of human experience, McLuhan wrote to Innis early in 1951:

One major discovery of the symbolists which had the greatest importance for subsequent investigation was their notion of the learning process as a labyrinth of the senses and faculties whose retracing provided the key to all arts and sciences… (Letters 221)

“The learning process” requires a resetting of experience. What the symbolists dis-covered according to McLuhan (citing especially Whitehead in this connection, but the general notion was vaguely in the air in the mid 20th century, hence the sudden appearance of cybernetics at that time) was that human experience is constituted, or perpetually reconstituted, through nothing else than such “learning”. Unlike physical materials whose being can be reset only through extremes of temperature and pressure, the notion here was that the being of human experience is continually reset via a momentary or synchronic katabasis into “a labyrinth of the senses and faculties”. This was to characterize the archetypal forms in terms of what was affected and, indeed, effected, by exposure to them: the variable shapes of “the senses and faculties”. There was no fixed orientation of the senses or faculties (the attachment to which defined the Gutenberg Galaxy); there was only a kaleidoscope of different configurations of these which became set through the synchronic process of ‘descent into the Maelstrom‘.

Exactly therefore, the “innumerable variants or ‘parti-colored’ forms” and “enormous number of combinations” of human experience. The ‘molecules’ and ‘compounds’ and ‘mixtures’ of experience resulted not only from diachronic interactions, like physical materials, but also, and above (or below) all, from moment to moment exposure to the entire range of experiential possibilities or forms and the resulting changes from this exposure. Human beings are exactly that type of being that is uniquely exposed to both these times at once.

As illustrated already by the 1918 observation of Joyce, itself doubtless related to Jung’s work at the time, and that to Freud and Frazer, modernity was the time when a resetting of experience was “learning” to focus on this resetting process of learning itself.  And it was doing so through a “retracing” of what had always already been retraced. 

Starting in the late 1940s, McLuhan began using Poe’s “Descent into the Maelstrom” as a figure of this synchronic process. At around the same time, he seems³ to have encountered Havelock’s two essays ‘Virgil’s Road to Xanadu’ (1946-1947) and ‘The Journey of Aeneas through the Waste Land’ (1949), in which a synchronic katabasis under the sea or into the underground is detailed in the literary environment of Virgil. At this time, too, he met Ezra Pound with Hugh Kenner and began an intense correspondence with Pound that lasted a full decade.  And, also with Kenner, he reread Eliot, again, especially Four Quartets, Pound, especially the Cantos, and Lewis (again) and Joyce (ditto). 

On other fronts, he continued his immersion in French symbolism (as Sigfried Gideon had recommended in 1944) resulting in his considerable unpublished manuscript ‘Prelude to Prufrock’. And, here prompted and assisted by his old Winnipeg buddy, Tom Easterbrook, he began as well his Auseinandersetzung with the work of Harold Innis and especially with his 1942 observation:

The concepts of time and space must be made relative and elastic and the attention given by the social scientists to problems of space should be paralleled by attention to problems of time. (‘The Newspaper in Economic Development’, reprinted in Political Economy in the Modern State, 1946)

The upshot of this vast and as yet inchoate complex of interests and influences was his developing notion of experience as a constant retracing of its principles or forms through a katabasis into their “worldpool”. Experience was always the result or effect of some selection out of that “worldpool” that McLuhan imagined in terms of the decision of Poe’s mariner in the Maelstrom to abandon his ship and to entrust himself, instead, to a “barrel”.

Now, rereading Joyce around 1950, this was exactly what he found in FW:

With Book III Wakean narrative turns back on itself to repeat “the seim anew” (FW: 215.23). If Book I could be said to move forward in the explication of HCE’s fate, then Book III moves backward. As Joyce explained to Weaver, the first part of Book III “is a description of a postman travelling backwards in the night through events already narrated. It is written in the form of a via crucis of 14 stations but is actually only a barrel rolling down the river Liffey”

FW research has paid some attention to Poe, both on account of his short story, ‘The Purloined Letter’ (1844), and on account of his influence on the symbolists via Baudelaire. But it may not have considered if Joyce’s “barrel rolling down the river Liffey” is Poe’s barrel in the Maelstrom. In any case, regardless of whether Joyce himself intended this connection, the vertical motion of Poe’s barrel reveals how Joyce’s horizontal “barrel rolling down the river” must be understood. Because time is “travelling backwards” here into the night of consciousness, and because it thereby revisits all “events already narrated” in their possibility (hence the need to abandon the language of actuality), such a barrel cannot be taken to disport itself in any fixed sense of “down”.  Instead, the coordinates of human action and experiences are here exposed as being just as relative as those of physical materials whose orientation depends entirely on the momentary perspective taken on them. (Hence the importance to relativity theory of Einstein’s thought experiments where, eg, clocks travel at the speed of light.)

What McLuhan discovered in Joyce⁴ at this time around 1950 was what he already knew from Mallarmé and Eliot and Pound.

Mallarmé discovered that the aesthetic moment of arrested cognition can be split up into numerous fractions which can be orchestrated in many discontinuous ways. (…) Joyce, Pound, and Eliot recovered the secret of the dolce stil nuovo [of Dante] through the prismatically arranged landscapes of Rimbaud and Mallarmé. And this secret consists in nothing less than a fusion of the learning and the creative processes [aka, of the genesis of experience] in the analysis and reconstruction of the aesthetic moment of arrested awareness. This peculiar fusion of the cognitive and the creative by an act of retracing the stages of apprehension was arrived at by Joyce as a result of the prior discovery for the technique of fission of the moment of aesthetic awareness. (…) In art as in physics fission preceded fusion. (The Aesthetic Moment in Landscape Poetry, 1951)

“The technique of fission” here was study of that synchronic “via crucis of 14 stations” through which experience is generated — ie, just what cybernetics was investigating at MIT (initially for the military) and what corporations were investigating for management training and marketing and what advertising agencies were investigating in their consumer research.

From his first years as a university student around 1930, McLuhan had been interested both in theory (aesthetics, epistemology and ontology) and in the practical world around him of education, entertainment, business and politics. Now, 20 years later around 1950, he found a way to bring these concerns together in the investigation of “the stages of cognition”:

Mallarmé wrote his most difficult poem, Un Coup de Dés, in newspaper format. He saw, like Joyce, that the basic forms of communication — whether speech, writing, print, press, telegraph, or photography — necessarily were fashioned in close accord with man’s cognitive activity. And the more extensive the mass medium the closer it must approximate to our cognitive faculties. (Catholic Humanism and Modern Letters, 1954)

What we have to defend today is not the values developed in any particular culture or by any one mode of communication. Modern technology presumes to attempt a total transformation of man and his environment. This calls in turn for an inspection and defense of all human values. And so far as merely human aid goes, the citadel of this defense must be located in analytical awareness of the nature of the creative process involved in human cognition. For it is in this citadel that science and technology have already established themselves in their manipulation of the new media. (Sight, Sound and the Fury, 1954)