This scanning electron micrograph shows four haploid spermatids forming as products of the final cell division in spermatogenesis. In the first meiotic division, a primary spermatocyte containing four complete sets of chromosomes divides into two secondary spermatocytes, each containing two copies of the genome. Often, the two secondary spermatocytes remain attached to each other. They each divide one more time (watch a video of this), creating four cells containing a single copy of every chromosome. Those four cells are the small rough spherical objects in the picture. Since mature sperm have a very simple role in life, fertilizing an egg, they don't need much of the biosynthetic machinery (e.g. ribosomes, endoplasmic reticulum, messenger RNA) or cytoskeletal components (e.g. microtubules and actin cables) typical of most cells. The large structure in the center is called a residual body. It is essentially a garbage bag into which the budding spermatids jettison all of their obsolete machines and molecules. After the spermatids have completely detached, the residual body and its contents will be degraded. Upon receiving a signal to complete their final differentiation, each spermatid will undergo a dramatic cellular reorganization, called spermiogenesis, to form a mature spermatozoon.