The term Umwelt (literally “around-world” or “surrounding-world”), which emerged as an important philosophical and biological term in the early twentieth century, has been defined in various ways. This paper first looks at the German biologist Jakob von Uexküll’s revolutionary notion of the animal’s Umwelt. It then explores the responses to, and critiques of, Uexküll’s notion of Umwelt: that of Ernst Cassirer, the German philosopher of Symbolische Formen (“symbolic forms”), and that of Martin Heidegger, the originator of Dasein (“being-there,” human being). It will be suggested here that, viewed on the synchronic axis of philosophical methods, their perspectives, though different, are fundamentally reinterpretations of the Kantian philosophy of logical form, the Kantian open-and-closed epistemological model. But it will also be suggested that Heidegger, with his hermeneutic circle of “understanding” and “interpretation,” comes closer than Cassirer to a view of the animal’s “around-world” that is congruent with Uexküll’s view of Umwelt.