An attempt has been made in the current paper to dispel two myths concerning Peter Simon Pallas, myths which have led historians of biology to distort the picture of some of the general biological ideas developed by that eminent naturalist of the Age of Enlightenment. The first point dealt with in the paper involves the myth that Pallas had allegedly drafted a 'tree of life' diagram, one of the many graphic representations of this kind to appear in later times, illustrating the structure of the organic world. The tree, of which Pallas merely left a short description (but not a depiction), took--in the articles of authors who wrote about it--a variety of graphic forms (largely dependent on the authors' pictorial inventiveness), with all the authors assuring the readers that they illustrated their reasoning with the help of Pallas's tree of life, but never mentioning that it was they themseIves who had drawn it. The current paper presents a juxtaposition of a number of such diagrams, drawn by different authors: the great diversity of the diagrams is sufficient proof that the existence of one, original 'Pallas tree' is just a myth. Another aspect of the myth has to do with the view that the tree supposedly illustrated phylogenetic dependencies - in fact, Pallas described affinity relationships between groups in the animal world. The present paper investigates how the 'tree of life' myth has developed, and reveals the mechanism that has most likely led to the myth being perpetuated in writings on the history of biology. The second issue discussed in the current paper relates to the myth of how Pallas's general views on biology allegedly evolved. The naturalist was supposed to have moved from transformism (characteristic of early stages of his work) to the idea of the immutability of species, formed in the period of his full scientific maturity. The current paper proves, inter alia on the basis of little known and not easily accessible writings by the scholar, that Pallas espoused the Age of Enlightenment's deism, an important element of which was the idea of the immutability of species, to which Pallas steadfastly subscribed. On the other hand, the analysis presented in the paper has revealed that Pallas seemed to consider the problem of species on two planes: that of free-roaming wild species, which remained absolutely immutable, and that of domesticated species, which did manifest some mutability, largely sustained by human effort but never transgressing species boundaries. It was also--and only--under domestication that monsters appeared. Pallas did contemplate, not without much hesitation, teratogenesis as a possible mechanism behind speciation, but--given the lethal character of monstrous modifications--he did not treat it as the real mechanism of speciation.