How do you make a tube? By rolling up a sheet. By extruding a tube from a plastic substance that then hardens. By drilling out a rod.
Now consider that a big animal such as ourselves needs lots and lots of tubes and pipes to carry nutrients and oxygen to individual cells and remove their waste. How does a developing embryo make all those pipes? Not by extrusion, surely. Rolling up a sheet doesn't seem likely. Maybe by forming solid cylinders of cells and then letting the central cells die off.
In the current issue of Nature, developmental biologist Makoto Kamei and colleagues for the first time confirm a longstanding theory in which cells form vacuoles -- internal bubbles -- which then fuse and merge into tubes. And they do it by making high-resolution time-lapse movies of the process taking place in vivo.
You can watch this amazing process here.
Which brings me to that old metaphor I have used a thousand times: Knowledge as an island in a sea of mystery. As we learn, the island grows, but so does the shoreline where we encounter the undiminished wonder of the world.