Herophilos lived between 335–280 A.C, and during that time had not invented the microscope yet, which was created by Zacharias Janssen in 1590.[2] The resolving power of the human eye is 0.1 to 0.2 mm, equivalent to a range of 100 to 200 mμ, while spermatozoa are microscopic size, where the head has an average length of 4 to 5 μm.[3,4] Therefore, Herophilos never could have said that the testes produce sperm, since these are not visible to the naked eye.