When the Academy dome was designed, the descriptive sciences of life had stabilized into zoology, which studied animals, and botany, which studied plants. Biology had come to mean both a laboratory science, as well as a more general term for a discipline that included many specialties or disciplines devoted to the study of living things. Zoology is the study of the animal kingdom, in all its variations and unique characteristics. This study requires large collections of living or preserved animals, which were part of many of the research institutions depicted elsewhere on the dome. The Museum at Alexandria in antiquity included both living and preserved animals, as did many similar institutions through the ages. Our modern museums and zoos have their roots in specimens collected during great European voyages of exploration from the Renaissance onward. We still think of animals as either backboned vertebrates (fishes, amphibians, mammals, and reptiles), or invertebrates, which lack backbones. These two classes are represented in the smaller images, shown by a zebra and a starfish. But the division, which followed from great debates in classification called "systematics" and "taxonomy" is imperfect. Various visible characteristics were used over the centuries, until evolutionary descent became the accepted criterion for classification. The zebra and the starfish, as many other animals, appear in very different relationships using other, historical classifications.