What was Leeuwenhoek talking about when he used the term " animalcules"?

1590s–1720s). Using single-lensed microscopes of his own design, van Leeuwenhoek was the first 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"]).
Parents: Philips Antonisz van Leeuwenhoek, Margaretha Bel van den Berch
Died: 26 August 1723, Delft
Born: 24 October 1632, Delft
Nationality: Dutch Republic, Netherlands

The independent variable is the type of music.the dependent variable is the pulse rate.the intervening variable is the age of the subject.if the mother does not like rock, her pulse is likely to not increase.the same might be true for the sister.the friend may like rap and gets excited.to establish cause/effect relationship, all of the subjects must be consistent.hope i .