Maximum fraction of semen is contributed by:

Some important points regarding spermatogenesis: Sperms are produced in: seminiferous tubules in testes. Sertoli cells nurture the developing sperms. Time for spermatogenesis: 64 days (Thymidine labelling records say it is 74 days). Normal sperm count: 20 million per ml or 40 million per ejaculate. Infertility is considered with a sperm count of less than 15 million sperms/ml. Fructose is the main source of energy for sperms. Prostaglandins suppress immune response against sperms in the female reproductive tract. Zinc serves to help to stabilize the DNA-containing chromatin in the sperm cells. Acrosomal cap houses the various enzymes needed to penetrate the zona pellucida of the oocyte.