A. Kent Christensen, Ph.D., Professor Emeritus, Department of Cell & Developmental Biology, University of Michigan Medical School

This section through a sperm in the testis of a terrestrial salamander (Batrachoseps attenuatus) was taken in an electron microscope. The animal was caught in the Arboretum of Stanford University in 1964. The large balloon-like pouch that looks like a parachute contains many small round structures called mitochondria. The mitochondria are energy factories that provide the sperm cell with sufficient fuel to actively swim.