Description: These are three differential interference contrast micrographs of bull sperm with protoplasmic droplets around the middle piece of the tail. Bull sperm heads are flat, about 10 microns long, 5 microns wide and 0.5 micron thick. The tail including the middle piece is about 60 to 70 microns long. It tapers from about 0.75 micron in diameter at the middle piece to about 0.25 micron at the proximal terminal piece. The sperm on the left has a proximal droplet, and the sperm on the right has a distal droplet (ie, at the end of the middle piece). The middle image illustrates a droplet about midway down the middle piece, and the tail is bent over the droplet. Often, sperm with the tail bent like this swim backwards. Normally, nearly all sperm in the epididymis possess a protoplasmic droplet on the middle piece of the tail. Nearly all of these droplets are lost by the time of ejaculation. While an occasional droplet on ejaculated sperm is no cause for concern, especially those located on the distal part of the tail, large numbers of protoplasmic droplets on the middle piece of ejaculated sperm indicate abnormal spermatogenesis or faulty epididymal maturation of sperm. Since this often forcasts reduced fertility, it is one of the signs technicians look for while evaluating semen quality in commercial artificial insemination laboratories. NAL #5087 illustrates greater structural details of sperm.