Sperm

The principal function of sperm is the delivery of their genetic payload, and other essential factors, to the female gamete. Yet multicellular eukaryotes have evolved a diverse array of morphologies to accomplish that simple goal. Sperm of some species are smaller than a typical mitochondrion while those of others are longer than the organism that produced them. In some species, they are vigorously motile while others are stationary… and do not forget about the tails, ranging from 0 to more than 50,000 per cell. This astonishing array of shapes and behaviors are likely to reflect adaptations to the range of environments in which these cells function. In many species, sperm are the only cell type that is cast outside the body to act in the external environment or within another individual, whereas males of other species – such as self-fertile hermaphrodites – do not share their sperm at all.