Answer:
Using single-lensed microscopes of his own design and make, Van Leeuwenhoek was the first to observe and to experiment with microbes, which he originally referred to as dierkens, diertgens or diertjes (Dutch for "small animals" [translated into English as animalcules, from Latin animalculum = "tiny animal"]).
Leeuwenhoek named the cells he observed originally as dierkens, which is the Dutch word for small animals, and translated to English as animalcules.
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