they described things the way they appear to the naked eye and he says the Halacha follows the appearance. Therefore even though we know today that lice DO come from eggs, they are still mutar to kill on Shabbos because the microscopic eggs are Halachically insignificant
I’m fairly certain that if you talk to any head-checker in a girls’ yeshiva, they will tell you that lice eggs are NOT microscopic. Small, yes — but not microscopic and they can be seen with the naked eye.
The Wolf