The dark seed looking things are in fact seeds; undeveloped ones.
A little background:
Wild bananas are diploid (two sets of chromosomes per nucleus)
Most cultivated bananas are triploid (three sets of chromosomes per nucleus) rendering them parthenocarpic (seedless) and incapable of sexual reproduction (sterile)
Wild bananas in fact form seeds, which are rather large and hard, and result in a banana which is not as easy to eat, hence we have seedless varieties and the elaborate means of reproducing them through shoots, root portions, or tissue culture.