WHAT ARE SPERM?
What is commonly thought of, as sperm is actually semen - the fluid ejaculated at the time of orgasm and it need not necessarily contain sperm. It is impossible to tell by its appearance whether the semen contains sperm or not. eg after a vasectomy a patient has perfectly normal ejaculation and there is no reduction in his semen. Yet, on examination, no sperms are seen in his ejaculate.
Sperm (or spermatozoa) are microscope creatures, which look like tadpoles swimming about a frantic pace back and forth in the semen. Each sperm consists of a head, containing all the genetic material of the father-to-be and a tail, which lashes back and forth at an incredible speed to propel the sperm along. In the ejaculate of a fertile man there are millions of these sperm, and they usually move at a very rapid speed.
More subtle and more important than the apparent frenzy of the movement is their purposefulness. Despite the fact that they are all moving in different directions (and so their motion appears to be haphazard and random), each one moves in a straight line with the accuracy of a guided missile. In a normal specimen each sperm that one sees goes straight across the without stopping, turning around, going in a pointless circle, and with no deviation from what appears to be a straight line.