A thank you to mudman@UBC Botanical Garden Forums for sharing this scan (original thread). Much appreciated!
Common stinkhorn can be found in the temperate forests and rich-soiled gardens of North America and Europe (and, according to Wikipedia, possibly southeast Australia). Of course, this image isn’t of the mature fungus (see: MushroomExpert’s Phallus impudicus for photographs). Instead, this is a cross-section scan of the immature stinkhorn, described succinctly in Wikipedia’s entry on Phallus impudicus:
“Sometimes called the witch’s egg, the immature stinkhorn is whitish and egg-shaped and up to 6 cm (2 in) in diameter. On the outside is a thick whitish volva, also known as the peridium, covering the olive-coloured gelatinous gleba. It is the latter which contains the spores and which later stinks and attracts the flies; within this layer is a green layer which will become the ‘head’ of the expanded fruit body; and inside this is a white structure called the receptaculum (the stalk when expanded), which is hard, but with an airy structure like a sponge. The eggs become fully grown stinkhorns very rapidly, over a day or two.”
For those who ask such things, yes, it is edible at this young stage, but it is not commonly eaten.
Lastly, a reminder that if you’re a fan of fungi, lichens and slime molds, there is an area of the forums dedicated to these beasties: Fungi, Lichens and Slime Molds Identification & Appreciation.