title: Ernst Haeckel's discovery of Magosphaera planula: a vestige of metazoan origins?
abstract: In September of 1869, while studying sponges off the Norwegian island of Gisoe, Ernst Haeckel (1834-1919) discovered a tiny, flagellated ball-shaped organism swimming about in his samples. Appearing first to be the planula larva of an invertebrate marine animal further observation revealed it to be a colony of flagellated cells with a complex life cycle transitioning between multicellular and single-cell stages and several distinct forms of protozoa. Haeckel named it Magosphaera planula (the "magician's ball") and it eventually assumed a central role in his theories of animal evolution, appearing as the modern exemplar of the blastaea stage in his gastraea theory of metazoan evolution. Throughout the latter half of the nineteenth century and into the twentieth it was an object of considerable scientific interest, and yet it was only ever observed by Haeckel himself and then only the once. Eventually it faded altogether from scientific discussion. This paper traces the rise and fall of Magosphaera as an important epistemic object in the theories of Haeckel and other biologists, and an attempt is made to identify what exactly the organism (or organisms!) was that Haeckel observed in the fall of 1869.
authors: Department of Philosophy and Religious Studies, Cape Breton University, Sydney, Canada.
authors: Andrew
authors: A
authors: Reynolds
authors: Norbert
authors: N
authors: Hülsmann
mesh_terms: D000818:Animals; D005075:Biological Evolution; D056890:Eukaryota; D005858:Germany; D049672:History, 19th Century; D006801:Humans; D008678:Metaphysics / Q000266:history*; D008954:Models, Biological; D009664:Norway; D010802:Phylogeny; D015046:Zoology / Q000266:history*