A lot of our understanding of early embryonic development came from experiments on two animals: Drosophila melanogaster (fruit fly) and Xenopus laevis (frog). Xenopus has huge eggs that are relatively easy to mark if you know what you're doing (I don't), so that's why they were so useful. One of the early questions that people wanted to answer was how do axes form. That is, how do you go from something round to something that has a front and a back, a top and a bottom?

It turns out that in Xenopus, the dorsal-ventral (back-belly) axis is determined by the sperm entry point! The side the sperm enters becomes the dorsal side, and the sperm creates a microtubule organizing center, essentially laying down tracks for the things that determine the ventral side to use to move over opposite the sperm entry point (now the dorsal side). When you destroy the microtubules (the tracks), the things don't move, and a dorsal-ventral axis doesn't form. But if you destroy the microtubules, and tilt your slide of embedded embryos so stuff sloshes around to opposite the sperm entry point, the axis is restored O.o

Obviously, the next question is what happens in space?* Do frogs develop normally in low-gravity environments? To answer this question, they took some frog embryos into space. If they didn't destroy their microtubules, the tadpoles developed normally...except they couldn't inflate their lungs until they were returned to a normal gravity environment. So, as NASA put it, "Failure to inflate their lungs would have had serious effects on the frogs at metamorphosis had they been kept at microgravity for multigenerational studies."

That is the story of the time we took some frog eggs into space.

*I am not at all sure how the first two paragraphs are relevant to the story, but they were in my notes. ETA: I am also not exactly sure in what order the experiments happened.