Armand Leroi gets a glimpse of a bishop's rectum

There is a cock with spurs grafted to its head, testifying to Hunter's belief in transplantation

hunterian museum, royal college of surgeons, lincoln's inn fields, london Tuesday to Saturday, 10am-5pm

The Hunterian Museum used to be a forbidding place. Dark and a little dreary, it was visited only by those with a taste for the macabre. But now, after a refurbishment that took three years and £3 million to complete, it is one of the most beautiful museums in the capital.

At its heart is the Crystal Gallery, an atrium two storeys high whose walls are made of glass shelves, on which sit thousands of anatomical specimens in bottles illuminated by hundreds of tiny halogen lamps. These specimens, shimmering in their solutions, are the legacy of 18th-century surgeon and comparative anatomist John Hunter. Here you can see the organic world, exquisitely dissected, system by system.

A list of just a few arbitrarily chosen items gives a flavour of the display: the brain of a mongoose lemur; the upper region of a lion's oesophagus; the gizzard of a Sumatran fowl; the second, water-carrying, stomach of a camel; a series of excretory orifices, including the cloacae of an iguana, a swan and an emu, the anus of a tapir and the rectum of Thomas Thurlow, Bishop of Durham (1737-91).

Although there are also displays of instruments and procedures, the heart of the museum is in the 18th century. There is a dissection of a torpedo ray showing the organs that Hunter and colleagues proved were the source of electricity - and that later inspired Alessandro Volta to invent the battery.

There is a cock with spurs grafted to its head, testifying to Hunter's belief that transplantation was possible and desirable, and a human testicle the size of an orange, testifying to his skill as a surgeon. The head and hands of a young chimp from Sierra Leone remind us that Hunter was also an evolutionist avant la lettre .

As I went round the displays, I tried to reduce them to order by identifying five favourite objects. These were: (1) a human foetus still enwrapped in its amniotic sac and chorion, as if in a skein of fine ivory silk; (2) the Evelyn Tables, a series of wooden boards to which have been varnished the complete nervous and circulatory systems of an 18th-century Paduan; (3) a Stubbs engraving of an amiable and wise-looking Indian rhinoceros; (4) the skeleton of Charles Byrne, the Irish Giant; and (5) the egg cases of sepia, the cuttlefish, resembling a cluster of berries, exactly as Aristotle described them.

I shall add another: (6) the severed foot of an infant girl displaying the lesions of smallpox. Since the disease is extinct, the foot is as important as a Dodo's skeleton - and the museum has one of those, too!

The astonishing thing is that this hoard of scientific treasures was, within living memory, far greater. On May 10, 1941, the Luftwaffe hit the museum, incinerating about two thirds of its contents. One can only rage to think what was lost.

After the war, the museum's curators attempted to restore the collection, accepting specimens from here and there. But after a while they realised the effort was futile. "Once an original has perished it has gone - whether this be a Hunterian specimen, a Rembrandt, a Winged Victory or anything else," said one, disheartened.

People whose aesthetic sensibilities are limited to art will find comparing a foetal sloth to a Hellenistic statue absurd. But they would be wrong.

Armand Marie Leroi is reader in evolutionary developmental biology at Imperial College London and author of Mutants , published by HarperCollins, Pounds 20.00.