Diatoms Arranged in an Exhibition Circle
This slide shows approximately 100 diatoms, which are the silica (glass) skeletons of single celled algae, shown in Darkfield. The background is black because the diatoms are lit not from directly below as is normally done, but from the sides using a hollow cone of light from a special kind of microscope condenser.
Per Wikipedia: Living diatoms number in the trillions: they generate about 20 percent of the oxygen produced on the planet each year,[12]take in over 6.7 billion metric tons of silicon each year from the waters in which they live,[13] and contribute nearly half of the organic material found in the oceans.
These have been arranged by an Englishman, Klaus Kemp, for display. Think of it as a flower arrangement, with each “flower” being an individual diatom. There are many, many different exhibition slides, by many different microscopists. Some are made with diatoms only as this one, some are made with butterfly wing scales, some are made with sponge spicules, some with radiolaria or foramnifera, and some are combinations
http://www.victorianmicroscopeslides.com/slideexb1.htm
https://en.wikipedia.org/wiki/Sponge_spicule
http://naturedocumentaries.org/15084/diatomist-matthew-killip-2014/