IN THE BRILLIANT concluding chapter of Hackenfeller's Ape, Brigid Brophy writes the soliloquy of an embryo ape awaiting birth, overfed, bored, and nauseated, resentful of its own confinement and eagerly looking forward to that of its mother. Some years ago I met a woman who said astoundingly that she had aqueous recollections of a similar life in the womb, but when pressed for detail she admitted that it had been even less eventful than that of the ape, rather like sitting in the waiting room of a dentist who is running behindhand on his appointments.

According to Richard Coe, Samuel Beckett recalls the moment of his own birth and dislikes the memory as much as he did the actual event. It is perhaps his greater age at the time of his first remembered experience that makes him recall it with such strong emotion, while the woman of my acquaintance summoned up only vague physical sensations equally unconnected with pleasure and the lack of it.

Such early memories, or at least assertions of them, are rare, although many other persons have claimed to recall events that happened not long after birth. If these accounts are to be trusted, they go far to prove the existence of pre-linguistic memory and to discount Wittgenstein's belief that conceptualization and memory are possible only when one has gained mastery over language. The conflict between these two theories lies at the heart of Coe's When the Grass Was Taller and is implicit in both the others here reviewed.

Written reminiscences of childhood and adolescence (awkwardly called ''Childhoods'' throughout the book) are the subjects of When the Grass Was Taller, The Art of Autobiography doesn't quite live up to its title, as it has a good bit to say portentously about autobiography, but in spite of the archiepiscopal heaviness of tone does not advance anything very profound about its art. A Book of One's Own is chiefly concerned with lives as recorded in diaries and journals. The pleasant truth, however, is that curiosity about the autobiographical impulse lies behind all three works, and they are all the better because they don't strictly confine themselves to their announced subjects and often poach on each other's territory.

THE AUTHORS of these three books are in accord that few diaries or autobiographies are written without at least a consideration of their being ultimately published, and surely most of them are in part gestures of defiance, fists shaken against oblivion. Beyond that, however, the reasons for writing them are many. In part they may serve as a reminder to the writer of his life, particularly in the case of diaries. For others they may be a form of egotism, asking for public notice of a kind they would not otherwise receive; since they are necessarily written within the lifetime of the subject, they may be occasionally a last desperate bid for recognition before death.

Probably the most interesting reason for autobiographical writing is the attempt of the writer to understand what has formed his own mind and personality. Almost inevitably this relies on memories of his early life, for most of us believe with Freud (although not necessarily because of him) that character is molded early in life, possibly even in he womb. As Cockshut writes, ''childhood is the most important time of all'' in the formation of personality. Coe tries rigorously to exclude any form of autobiography that isn't confined to the early part of his subjects' lives, and in Mallon's studies of diarists, childhood is a recurrent subject, although the diaries he examines were chiefly written by adults.

Cockshut deals with some 50 autobiographies, many of them comparatively minor, since he has considered more important examples elsewhere. In the course of Mallon's book he mentions approximately 200 diaries that he has read. Coe says that his conclusions are drawn from 600 examples of ''Childhoods,'' but we have to take his word on the matter: their names are not recorded here but in a periodical article he has written on the same subject.

Faced with such a daunting amount of raw material, all three writers, university teachers to a man, take the traditional academic escape route of classification, and try to reduce the unruly mass to a tractable series of categories within which a group of stubborn individualists will exist in harmony. It doesn't work, of course, because the subjects are as unlike each other in print as in life, and they constantly burst through such slack headings as ''Pilgrims,'' ''Creators,'' and ''Apologists'' (Mallon), or ''The Child Alone,'' ''The Child at Home,'' and ''The Quest'' (Cockshut). I suspect all three authors feel some unexpressed relief that their subjects are too lively to suffer such narrow confines.

Unlike the others, Coe considers fiction as autobiography in his theoretical work, naturally using Proust and Joyce, but making his net with such a fine mesh that in the cases of Alain Fournier's Le Grand Meaulnes, Dickens' David Copperfield, and D.H. Lawrence's Sons and Lovers, Coe must ''regretfully assign the work to the domain of fiction.'' It is not clear why they must be excluded from consideration when Portnoy's Complaint serves as an example; Philip Roth has understandably never, to the best of my knowledge, acknowledged it as a direct record of his own experience (or experiences). And what reader ever took it as a more autobiographical work than David Copperfield?

ALL THREE writers shy when brought up to the hurdle of deciding the relationship between overt fiction in the novel or short story, and the subtler form of it achieved when the autobiographer departs from the verifiable pattern of his life, as he must in giving shape to his memories. This seems a particular shame in Coe's book, since his major point is that reminiscences of childhood deal with a country remote from the adult state and that they can be recorded only in the poetic language of that land.

Of these three volumes, A Book of One's Own is the most thoroughly successful, fully achieving its unassuming intention of introducing us to some of the writers who have given Professor Mallon pleasure, and of indicating the flavor of their diaries. It is a delightful book, and it would be a mistake if his relentlessly jolly schoolboy style made a reader put it down. On only the third page, for example, he writes of Pepys, ''Along with a great job, he's got a swell wife.'' But it's worth persevering for another 300 pages, even though there is a good bit of that kind of cozy, chatty facetiousness to slog through, for he makes us want to read most of those diarists we don't really know.

Of course we expect, and find, Dorothy Wordsworth, the brothers Goncourt, Boswell, Virginia Woolf, Parson Woodforde, Alice James, Thoreau, and Anais Nin all scribbling away, and a pleasure they are, as always. But what is even better is coming across names of whom we have never heard. For me the find of the book is Bruce Frederick Cummings, whose pseudonym was W.N.P. Barbellion, a monstrously, almost crazily, egotistic scientist who spent his days in the Natural History Museum in South Kensington, and his nights in pouring out to his diary a flood of vituperation at a world that continued its even tenor even though he was dying of disseminated sclerosis. All his black energy was turned on death as it secretly stalked nearer and nearer: no resignation for him, ''Even as I sit and write, millions of bacteria are gnawing away at my precious spinal cord, and if you put your ear to my back the sound of the gnawing I dare say could be heard.''

A vitality that would have furnished a dozen ordinary men was confined in his constantly wasting body, compressed into 30 brief years of life, all too short a time, as he knew, to taste the sensations of existence. As Mallon writes, shocked for a moment into sobriety of style. ''In a genre to which it is impossible to ascribe formulas and standards, he forces one to render a judgment -- namely, that his is the greatest diary a man has written.'' As soon as I finish writing this review, I intend to begin reading The Journal of a Disappointed Man, the book he published in 1919, only a short time before he went out still fighting.