Nature & living systems
Three hearts. Two work the gills.
Two hearts pump blood through the gills. A third sends oxygenated blood through the body.
The idea
Counting parts tells less than understanding how the parts divide the work.
An example
A simple flow sketch can separate the gill-related role from the body-circulation role. The useful insight is that “three hearts” is an arrangement of functions, not three interchangeable copies doing an identical job.
Try it
Explain the fact without using the number first. Start with what the different hearts do.
More context
Two move blood through the gills. The third sends oxygenated blood through the body. Its copper-containing oxygen carrier, hemocyanin, gives oxygenated blood a blue color. Biology · octopus circulation
Sources & further reading
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