Rudolf Leuckart (1822–98) was a respected zoologist and parasitologist. He lived in the heyday of the 'new zoology', which was influenced by both darwinism and the new discipline of physiology, and was increasingly scientific in its approach.

At a time when the life cycles of organisms were just starting to be understood, Leuckart was at the forefront. In one notorious experiment, for example, he found a volunteer to swallow four cysticerci, the larvae of the human tapeworm, to prove that these 'bladder worms' would develop into tapeworms using the human as host. One month later, the unfortunate volunteer was duly purged of two 2-metre tapeworms, and the prevailing concept that such parasites were generated spontaneously was finally laid to rest.

But Leuckart, who became rector of the University of Leipzig in 1877, left just as powerful a legacy in the form of his didactic Wandtafeln, or wall charts. The use of large scientific wall charts as teaching aids became popular in universities in the second half of the nineteenth century. The fashion followed the introduction of Wandtafeln in German schools as part of broad educational reforms inspired by Johann Heinrich Pestalozzi, who believed that children should see and experience, rather than learn by rote. Zoological wall charts in particular were valued at universities around the world.

Leuckart's beautiful series was neither the first nor the last to be produced, but is arguably the most significant, particularly given its extensiveness. There were 101 wall charts in his series on invertebrates, although the second series, on vertebrates, co-edited by his younger colleague Carl Chun, peters out after just 12.

The artwork was mostly produced by a series of Leuckart's assistants, who inevitably needed artistic as well as scientific skills. Leuckart himself illustrated only one of the charts with his own hand, that of his tapeworm (shown on the right). Each chart presents a single species, depicting its anatomy in different stages of growth or life cycle, and often alluding to function.

Their styles vary somewhat. But the 22 artist-zoologists all owe a debt to their contemporary Ernst Haeckel, a vociferous promoter of Darwin's new theory of evolution, whose superbly composed and beautifully drawn illustrations revolutionized the presentation of zoology. Haeckel used some of his own charts in his public lectures, happily compensating for his reportedly poor verbal skills.

Leuckart 's wall charts are not labelled with any explanatory text. Detailed explanations are instead provided in pamphlets intended for teachers, in three languages: German, English and French.

Production of the charts was technologically challenging and labour-intensive. Their size — 1 metre by 1.4 metres — required that they be printed in four sections, before being joined together and touched up. A complete set cost more than twice as much as the most expensive microscope of the time, yet they sold widely.

Unfortunately, very few of the charts have survived. So the discovery in 1997 of an almost complete collection, with full explanatory texts, at the University of Pavia in northern Italy is exciting. The charts were found when several of the university's science departments moved out of the eighteenth-century Palazzo Botta, where they had been situated for more than two centuries, into modern laboratories. Cleaning out long-forgotten attic and cellar stores, zoologist Carlo Redi stumbled across a large, 18-drawer chest in which the charts had been collecting dust for decades. The invertebrate series is complete, and only three charts in the vertebrate series are missing; these have since been located in Hamburg.

Only one other nearly complete series with explanatory texts is known to exist. It is held at the Marine Biological Laboratory in Woods Hole, Massachusetts. Again the invertebrate series is complete, but four charts are missing from the vertebrate series. Some 40 individual charts have been located in Hamburg, Leipzig, Rome and Padua.

The Woods Hole collection is available digitally on the laboratory's homepage. The Pavia collection has also been digitalized and has just been published as a sumptuous book, Visual Zoology, with an accompanying CD. Redi hopes to make the collection available on the University of Pavia's homepage soon.

The Pavia collection can be seen in Visual Zoology: The Pavia Collection of Leuckart's Zoological Wall Charts, 1877, edited by Carlo Alberto Redi, Silvia Garagna, Maurizio Zuccotti, Ernesto Capanna & Helmut Zachirias (Ibis, 2002).

Woods Hole collection → http://www.mbl.edu/leuckart