Complex sentence: Sebaceous glands are concentrated on the forehead and dispersed on the torso of dominant males; these glands males are most active during the mating season, while those of females are only partially developed and do not undergo seasonal changes.
Split into simpler sentences: Sebaceous glands are concentrated on the forehead and dispersed on the torso of dominant males. The forehead glands present in males are most active during the mating season, while those of females are only partially developed and do not undergo seasonal changes.