The seminal vesicles are two bags located close to the ampullae behind the bladder, near the tip of the prostate. Originally it was assumed that the seminal vesicles were there to store the newly formed spermatozoa. Today, however, it is widely believed that their main task is to produce a fluid that, together with prostate secretion, ensures sperm motility after ejaculation.
https://de.wikipedia.org/wiki/Bläschendrüse (Wikipedia CC-by-sa-3.0)