I like liquids, I have been studying them since my PhD. Mainly I have been trying to understand them, but many scientists and engineers study them because they are so useful. Over the last 10 to 20 years people have been developing what is called microfluidics, which is kind of playing around with lots of little droplets. But these droplets can be very useful. Each droplet may contain only a trillionth of a litre, and be only a hundredth of a millimetre across. But still the people who work with them can do a little experiment in a single one of these droplets.

This is impressive, but it seems that the idea of using little droplets has been around for some time, maybe 100s of millions of years. Because it appears that the idea of microfluidics, of working with tiny droplets, has been hit upon in nature.

Here is a movie of some cells from an embryo of a tiny worm called by its Latin name C. elegans, i.e., the movie is taken of the inside a small animal. Note the bright droplets that are present and flowing to the left. You can’t see where one cell ends and another begins here but the droplets are clustered around dark circles and each dark circle is a nucleus. There is one nucleus per cell. The movie is from a really cute paper by Brangwynne et al.

In microfluidics, the liquid droplets are typically oil droplets in water, or the reverse, water droplets in oil. The droplets in C. elegans are a bit different. Both the droplets and the surrounding liquid in the rest of the cell are mostly protein in solution, but the proteins in the droplets are different from those in the rest of the cell.

The liquid droplets in the cells, like those in microfluidics, have a function. They are required to specify which cells will go on to be the sex cells and produce the sperm and the eggs. The cells with these droplets go on to do that, while the cells that don’t form the rest of the worm’s body, like the muscles, nerves, etc.

So without these droplets, there would be no boy meets girl, or rather boy meets hermaphrodite as the two sexes in C. elegans are male and hermaphrodite.