THE RESPONSIVENESS of Irving Wallace to the shared fantasies of the largest reading public (at least of his generation and mine) is attested by a jacket blurb assuring us that his works "have sold more than 112,000,000 copies world-wide." And we can take it then that somewhere in those fantasies Chang and Eng, a pair of joined twins dead for more than a century, still live the posthumous life of other mythological Americans, who, in one way or another, Made It Big - like P.T. Barnum, Charles Lindbergh, J.P. Morgan and Abraham Lincoln. In the last decades of the 20th century, they haunt not just the aging among us, but even more perhaps the freak-obsessed young; so that it seems appropriate that the present volume be co-authored by Wallace's daughter, Amy, the "psychic healer."

Not only have such favorite writers of the moment as Vladimir Nabokov and John Barth created eerie and comic fictions based on their case, but even more recently Donald Newlove (twice over) and Judith Rossner have written novels about inseparable siblings forever unsure whether they are two or one. Even the National Lampoon has run a continuing comic strip about a particularly feckless pair of similar anomilies, called after their legendary prototypes "Siamese Twins."

Yet ever since the late "50s, most such twins have been surgically separated and have survived. Indeed, the special pathos of the plight of Chang and Eng from the vantage point of 1978 is that they could have been safely separated; and that they were therefore not, as they thought themselves, the victims of inexorable fate, but merely of the technological backwardness of their era. And this may, in facct, explain their renewed and altered appeal.

The first American novelist to become obsessed with Chang and Eng - as the Wallace, who tell us nothing of their later literary uses, do report - was Mark Twain. In the beginning, they provided him with occasions for heartless travesty and ebullient bad taste. But he could not exorcize them with brutal flippancy, and his continuing meditation on them and others like them (most notably the Tocci Brothers who had four arms but only two legs) helped create the fantasies on twinning and duplicity which make his Pudd'nhead Wilson the great failed book it is.

Even earlier, writers had appeared who were more interested in presenting the Twins in terms of fact rather than fiction. And this seems fair enough in light of their relentless drive to embed themselves in the prosaic, the everyday, the ordinary - to normalize their fabulous life/lives. To be sure, their birth in Siam (where they were known as the "Chinese Twins," strangers in a strange land from the start) was greeted as uncanny, and they were almost killed in superstitious awe. Surviving, they were exported as Wonders, then exhibited as "curiosities" until at 21 they were free to determine the direction of their own careers.Before being acquired by foreign traders, however, they had already established themselves as boy-merchants; and once they had become their own masters, submitted to being shown only under the direst economic pressure.

They married, had children (21 between them), set up separate households, operated separate farms, owned slaves, kept accounts, played cards and checkers, smoked cigars and pipes, drank, brawled, voted, talked politics and gave two sons to the Confederate Army - all under the super-American name of Bunker. They turned themselves, in short, by will, wit and sheer energy into good citizens as defined by the rural North Carolina community into which they were finally accepted. Accepted. It is a success story with which we are familiar: the Making of Americans out of immigrants. Think though of the odds against them. They were not just Orientals in a homogeneous WASP world, but anomalies, doomed forever to lie three in the bridal bed, where all their decent neighbors knew there should be no more than two.

No wonder they sought always the operations that would really normalize them; deliver them from a shameful bondage more absolute than slavery (one can imagine the fury of their fourhanded flogging of the black chattels whose indignity seemed less ultimate than their own), as well as the till-death-do-us part union which made a mockery of their less indissoluble marriage to two wives, each of whom weighted more than the two of them together. Even in death, Chang and Eng sleep together, but their wives are separated - only one heap of female bones apparently having been laid to rest beside theirs, despite the misleading inscription on their monument. One wife for two husbands . . . Or were they ever really, really two?

For a long time they seem not to have been sure, signing themselves chang-Eng or Chang-Eng, and their earliest letters referring to themselves indifferently as "I" or "We." Later, they differentiated themselves as much as they could, one becoming ever more passive, one ever more aggressive, one ever drunken, the other ever more disapprovingly sober; until they had achieved - in final travesty of a bad arranged marriage - an exacerbated incompatability from which neither could escape. When Chang, therefore, from whom he had tried so long to divorce himself, died of a stroke, Eng also died - of fright, said the physicians at a much publicized postmortem. But fright of what, they did not say, leaving us to speculate: fright of freedom? Of deliverance from long habit and indurated love/hate? Of the prospect of unaccustomed loneliness?

It is scarcely surprisingl that so tantalizing a tale has attracted journalists and chroniclers ever since Chang and Eng first began to appear on the stages of the world. In addition to numerous articles, there has been a series of biographical books beginning in 1853 with what was scarcely more than a publicity pamphlet and climaxing in 1964 with a full-length popular study [LINE ILLEGIBLE] Duet for a Lifetime. Even her book seems disconcertingly sketchy, however, and much relevant information has remained unavailable to the general reader, since accounts written by men who actually knew the Twins never got out of manuscript or were privately printed in limited editions. But the Wallaces have read it all, along with old diaries, letters and fugitives pieces in the contemporary press, compiling with patience and tact the fullest story of their lives we are likely ever to have.

It would, therefore, be churlish to complain that they have failed to explore in depth the symbolic resonance of what they hace compiled. The simple facts move us like a troubling dream, even without interpretation. And we are left free to meditate for ourselves about the new light they cast on the naturalization of Americans, the ambiguity of success and failure and especially on the mystery of identity: the uneasy revelation experienced by Mark Twain (but surely not by him alone) in the presence of such Twins; the awareness that in all of us there lives a "double," a "partner in identity," an "other and wholly independent personage" whose death would entail our own.