THE EARLY PART of the 20th century saw a great revival of interest in the bestiaries, or medieval books of beasts, and their sources. Sadly, it seemed necessary to the writers of those days to expunge everything even vaguely indecorous, and the results were unbelevably dull. One might as well attempt to expurgate Chaucer's "Miller's Tale"; to do so would rob it of an essential characteristic. Small wonder that these quaint books subsequently were neglected.

But the bestiaries make fascinating reading. Indeed, many allusions in the works of shakespeare and his contemporaries are inintelligible to the reader without a working knowledge of the animal lore of the Middle Ages. It is therefore a special pleasure to find two new books which are closely allied to this subject.

The medieval bestiaries were produced by monks not only to disseminate zoological data, but to paint a Christian moral. Though Christian in concept, they were founded on material dating back to pagan eras. Their immediate source, however, was a book called Physiologus , which enjoyed an immense popularity from its original composition in the fourth century, survived a ban purportedly imposed by Pope Gelasius late in the fifth century, and was only ousted from public favor after the 11th century, when the fuller accounts in the bestiaries superseded it.

Physiologus, translated and with a scholarly introduction by Michael J. Curley, is, surprisingly, the first complete translation of this work in the English language. In introducing his subject Curley gives a careful account of the history and development of Physiologus, including the insoluble problem of its authorship. The text itself details the supposed characteristics of 51 beasts, stones and plants, real and imaginary. Perhaps most extraordinary is the legendary ant-lion, the supposed offspring of a male lion and a female ant. This curious hybrid had a very short life span. Its front half was carnivorous, like its father; but its stomach was that of the herbivorous ant. Starvation after a few days was its only possible fate.

Belief about the weasel was almost equally curious. It was forbidden as food, because its mating habits were considered unclean: The female receives the seed of the male in her mouth and, having become pregnant, gives birth through her ears . . . Wicked things are engendered through the ears." The hyena, too, was considered a filthy beast, for it was believed to change sex each year. The beaver, whose genital secretions were sought as medicine, seeing the approach of the hunter, "bites off his own genitals and throws them before the hunter . . . If you have had evil inclinations toward sin, greed, adultery, theft, cuth them away from you and give them to the devil," admonishes the writer.

But an even greater joy than Physiologus is The Elizabethan Zoo, a revival of the 1926 edition of a selection from the works of Edward Topsell, whose Historie of Foure-Footed Beastes (1607) and Historie of Serpents (1608) were drawn upon by Shakespeare in his final years. Topsell's books were really translations of the works of the Swiss naturalist Conrad Gesner, supplemented by material from Philemon Holland's 1601 translation of Pliny's Natural History. This short selection by M. St. Clare Byrne manages to convey much of the spirit of the gigantic originals.

Of particular charm is the description of the elephant, which "is delighted above measure with sweet savours, oyntments and smelling flowers," so that it will "chuse out and gather the sweetest flowers . . . and will not eat meat until they take of their flowers and dresse the brimmes of their maungers therewith."

Topsell's legendary mantichora, with its triple row of teeth, its scorpion stingers in the tail, and its partiality for human flesh, seems to possess the typical Edwardian face, complete with beard and mustache. Topsell's Gorgon, a native of Libya, continually hangs his head; which is fortunate, for if he raises it, he "sendeth forth of his throat a certaine sharpe and horrible breath which infecteth and poysoneth the air above his head, so that all living creatures which draw in the breath of the aire are greevously aflicted thereby, loosing both voyce and sight, they fall into leathball and deadly convulsions."

The splendid drawing of the rhinocerous is pirated from Durer (Gesner gives Durer credit; Topsell does not). Topsell says of this beast, "Hee is taken by the same means that the Unicorne is taken, for it is said . . . that above all other creatures they love Virgins, and that unto them they will come be they never so wilde and fall a sleepe before them, so being asleepe they are easily taken and carried away." This is a legend common to many horned beasts, real or imaginary, and to the elephant also.

But most curious of all are the cockatrice, supposedly hatched by a toad from a cock's egg, and able to kill at a glance, and the many-headed hydra, whos existence even Topsell questions. The illustrations throughout are quaint and help to convey the nature of Elizabethan natural history.

Elizabethan zoo will prove a source of delight to many. Perhaps it will stimulate some of its readers to delve more extensively into Topsell's original works.