39: That’s how many times per minute a sleeping Cassiopea jellyfish pulsates, according to new research. (They pulsate about 58 times per minute when they’re awake.) The experiments that Caltech researchers conducted — which involved poking the spineless, brainless critters to keep them alert — suggest that sleep is a surprisingly ancient phenomenon. The biomechanics of sleep are not very well understood, so the dozing Cassiopea raises lots of new avenues for future study. For instance, if something as primitive as a jellyfish can sleep, can plants?Alex Kingsbury can be reached at firstname.lastname@example.org.