The history of heat versus temperature is quite enlightening. The absence of thermometers means you have a hard time conceiving of heat capacity. They knew that phlogiston wasn't right but all of their experiments kept assuming it was measurable. Same with mass versus weight; the difference isn't hard to measure once it occurs to you to measure it.
These can be great aha moments in the history of science. It's both daunting and inspiring.
Much more recently I heard on QI about how medieval people, not knowing about migration, believed, through a lot of leaps, that it was ok to eat barnacle geese at lent. Worth investigating if you are curious :)
I think illustrations or stories from the middle ages are to be taken as symbolic or allegorical rather than factual like a biology book would be today. They wrote down a story not because they necessarily believed it be factually true, but because it taught a different kind of truth. For example, no one has ever believed that Red Riding Hood actually happened or that you can cut open a wolf's stomach to pull out a living person.
You can guess that now in the 21st century, but we're talking about illiterate peasants who never traveled past their nearest market center. It's naive to assume you can even possibly empathize with their epistemological outlook.
For example, just look at the medieval sources about barnacle geese from the 13th century (from the educated class):
> Barliates, as Aristotle says, grow from wood, and are birds which the common people call 'barnesques', having a similar nature. [1] (I chose a short quote to make a point but please read the rest of the source, it's hardly an allegorical text)
They didn't have the concept of falsifiability or anything even remotely resembling the scientific process (or critical thinking, for the most part). The literate were obsessed with the classics and just took Aristotles and Ptolemy's word for everything, until Copernicus and Kepler had their way. Anything resembling scientific knowledge filtered down to the peasants or came from old wives tails entirely.
Even now with almost universal literacy we have a significant fraction (if not majority) of the population believing in ridiculously stupid nonsense like astrology. I don't find it hard to believe that people thought that geese's life cycle included barnacles.
[1] https://www.medievalbestiary.bestiary.ca/beasts/beastsource1...
Medieval Science was Baffled by Birds - CuriousCabinet123
> The researchers behind this recent discovery used satellite tags to follow 21 female European eels as they navigated the final phase of their incredible journey southwest from the Azores, the volcanic archipelago of the North Atlantic Ocean west of Portugal.
> questions remain about the timing and navigation of the eels across thousands of kilometers of open water
Makes me wonder what the world was like before this last great extinction.
[0] https://www.nature.com/articles/s41598-022-19248-8
I sometimes think about the selection pressures that lead to complex life cycles, like fig wasps. I find myself thinking about it naively, like one existed and the other grew into the niche. But, realistically, everything is changing (slowly) all the time. I just notice it for, say, influenza because their cycle time is so short.
The answer itself is interesting, but more remarkable to me is how doggedly people pursued it for so long. It seems so basic that they must reproduce the way other vertebrates do, and yet the lack of apparent organs was baffling.