hairs which are constantly 'sweeping' in a forward motion to sweep the egg into the tubes and help it travel forward down the tubes. Unlike sperm, eggs do not have any motility on their own so need some help. These hairs (cilia) keep the sperm from heading through and out of the tubes. It is important for the sperm to be in the tubes in advance of the egg. WHile in the tubes there is an enzyme which causes a change in the sperm which allows it to penetrate the egg casing. So... don't worry about the sperm escaping!!!
Your question was a good one and totally logical!!