Now my tomatoes are in flower, and I have taken some photos of the flowers. Note the stigma protruding from the anther “barrel”, seriosly increasing the risk of having a cross with another tomato variety. Often it will fertilize itself, by dust dropping from the anthers to the stigma – just remember the risk/chance.
In the ordinary leaved tomato flower, the stigma is not long enough to reach out of the “barrel” of anthers. Insects rarely interfere with the stigma thus set in its private little “dusting chamber”.