Explanation

In spermatogenesis, during growth phase some spermatogonia either due to growth or due to food storage become 2 or 3 times large of their original size and are known as primary spermatocytes, which undergo meiosis-I and as a result 2 haploid secondary spermatocytes are formed. Futher, meiosis-II takes place that results in the foramtion of 4-spermatids. Then, these round, non-motile and haploid spermatids are transformed into thread-like motile, haploid (four) sperms.