The medieval simile of the world as a book seems to anticipate modern notions of biodiversity as a key to insights and learning. This thought is translated into the practice of research in the August Krogh principle, which provides argumentative support for researchers who dare to venture beyond the range of commonly used models by choosing a new experimental organism for a particular scientific question. Established model organisms often hold high exploratory power to the researcher yet little explanatory power to the student, in particular when represented in a secondary source. This essay puts forward the suggestion that Krogh's principle applies to the use of organisms as instructional models and textbook examples too and encourages educators to continuously venture beyond established illustrative teaching examples in a continuous exploration of the "book of the world" and the "treasure house of nature."