What did Leeuwenhoek predict was within the heads of these little tadpoles?

Leeuwenhoek predicted that within the heads of the little tadpoles, there were tiny, developing organisms, which he referred to as "little animals." He observed their structure through his microscope and suggested that these creatures would eventually grow into fully formed tadpoles. His observations laid the groundwork for later understanding of embryonic development and the study of microscopic life.