Please modify this text to be simpler:
Using single-lensed microscopes of his own design, van Leeuwenhoek was the first to experiment with microbes, which he originally referred to as " animalcules " (from Latin " animalculum " = " tiny animal ").
Using his handcrafted microscopes, he was the first to see and describe single celled organisms, which he originally referred to as " animalcules ", and which we now refer to as microorganisms.