n this text, what are to be considered three fundamental aspects of the concept of Umwelt proposed by Baltic biologist Jakob Von Uexküll are problematized. Such aspects are (i) the way this concept helps battle the mechanistic and reductionist tendencies of the study of nature by the aid of Immanuel Kant"s Transcendental Aesthetics, (ii) the manner in which it establishes an study of living beings form the subjective point of view, and, finally, (iii) the form the groundworks of Uexküll´s production allows the foundation of an horizontal ontology of the animal world, which includes equally all living things, all of this trough the rescue of Uexküll´s writings that Martin Heidegger carries out in his 1929 winter lessons The Fundamental Concepts of Metaphysics. World, Finitude, Solitude. I