Fine structural observations on the development of the sperm head in the mouse

The stages of spermiogenesis in the mouse were investigated with the electron microscope with emphasis on morphogenesis of the sperm head. The nucleus undergoes chromosomal condensation in the concluding stages of spermiogenesis. Chromosomal condensation proceeds centrifugally and in a caudal direction, beginning in the anterior third of the nucleus. It is proposed that chromosomes establish attachments to the nuclear envelope prior to the onset of chromosomal condensation and that this arrangement of the chromosomes is an orderly one which facilitates the condensation process.