the sperm's cell membrane then fuses with the egg cell's membrane, and the contents of the head diffuse into the egg. upon penetration, the oocyte is said to have become activated. it undergoes its secondary meiotic division, and the two haploid nuclei (paternal and maternal) fuse to form a zygote. in order to prevent polyspermy and minimise the possibility of producing a triploid zygote, several changes to the egg's zona pellucida renders them impenetrable shortly after the first sperm enters the egg. artificial storage spermatozoa can be stored in diluents such as the illini variable temperature (ivt) diluent, which have been reported to be able to preserve high fertility of spermatozoa for over seven days. the ivt diluent is composed of several salts, sugars and antibacterial agents and gassed with co2. semen cryopreservation can be used for far longer storage durations. for human spermatozoa, the longest reported successful storage with this method is 21 years. mmp and capacitation the capacitation is the final phase of spermatozoa development, when they acquire the capability to fertilize the oocyte. in vivo, it happens during ejaculation, when spermatozoa leave the vagina and come in the superior female reproductive tract. in vitro, it happens when the spermatozoa is washed and purified. almost 30-40% of infertility is due to male factor, so several strategies have been created in order to recover the functional spermatozoa. the mmp (million motile progressive cells per milliliter) measure is synonymous with capacitation, and is very useful parameter to decide, along with a spermiogram, the kind of treatment needed. it represents the ratio between the % of progressive motile sperm obtained in capacitated and the % of progressive motile sperm obtained in ejaculated. it is based on the recovery percentage. depending on the percentage, we will decide the quality of the motile spermatozoa recovery: 15 to 25 million sperm/ml is considered optimal, between 5 and 15 million is considered enough and less than 5 million is considered sub-optimal or not sufficient. regarding the values that we have obtained, along with the spermiogram results, different techniques will be displayed. for example, if more than 1.0×106 progressive motile sperm per milliliter are found, it will be recommended to have sexual intercourse, and if that fails, the next step will be intrauterine insemination and later conventional in vitro fertilization. with less than 1.0×106 progressive motile sperm per milliliter, we will perform intracytoplasmic sperm injection. in case of azoospermia (no spermatozoa in the ejaculate), we will do a testicular biopsy in order to check if there are spermatozoa in the testes or if no spermatozoa are being produced. history in 1677 microbiologist antonie van leeuwenhoek discovered spermatozoa. in 1841 the swiss anatomist albert von kölliker wrote about spermatozoon in his work untersuchungen über die bedeutung der samenfäden (studies on the importance of spermatozoa).