 Zend-Avesta is Fechner’s most personal work, the statement of his fundamental beliefs. It is nineteenth century metaphysics in the grand style, on a par with Schopenhauer’s Die Welt als Wille und Vorstellung and Lotze’s Mikrokosmus. It is a much more ambitious work than Nanna. Whereas Nanna would deal strictly with the realm of botany, Zend-Avesta would consider the cosmos as a whole. While Nanna would prove only that plants have souls, Zend-Avesta would attempt to show that the entire organic universe has a  soul.[10]  Although this panpsychic doctrine was the inspiration for Nanna, Fechner, as we have seen, refused to make it the basis of his argument. Now, in Zend-Avesta, it will be his purpose to prove this doctrine. 