Both vesicles are about 5 cm in length, but they are curled up. Each gland makes a ball shape on the wall of each vas deferens. There is a tube linking the seminal glands which opens into the vas deferens and prostate gland.
From inside to out, the layers making the vesicles are:
The seminal vesicles make most of semen, but during ejaculation, most of the ejaculate has sperm rather than semen in it. The use of seminal fluid is not known, since sperm do not move or survive well in semen. Some think that it acts as a fluid to stop sperm from another male impregnating the female so that the children of only one male can survive.