While tracking their development, we've been consulting Steven Osborn's master's thesis — Fecundity and embryonic development of Octopus rubescens Berry from Monterey Bay, California. In one section, Steven wrote, "Embryos reverse their position twice during development...The first inversion occurred at Stage 17-18. The second inversion occurred at Stage 29-30."
We were too late to see the first inversion (we didn't start watching until about Stage 19). But we knew the second inversion was due. When I looked at the embryos today (Day 69), I was a little surprised to see that many of them had inverted overnight! The easiest way to see this is to look at the position of the eyes and whether they're closer to the broad, rounded end of the capsule (as above)...or closer to the narrow, pointed end (as with many of the embryos below).
Now I'm nervous. I'll be away for a week, and luckily we have good octopus-sitters. But hatching might not be too far away! We were estimating it would happen sometime in October (and it still might), but if water temperatures have been warm, development may be faster.