Complex sentence: Changes may be the result of the release of the contents of the club cells; these cells do not open directly to the surface of the skin, but injury caused by fighting and other agonistic behaviors may release the cells contents.
Split into simpler sentences: Changes may be the result of the release of the contents of the club cells. These cells do not open directly to the surface of the skin, but injury caused by fighting and other agonistic behaviors may release the cells contents.